SB 741 RE BLIGHT DISEASE IN NURSERY STOCK 

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Copy 1 



A THESIS 

Presented to the Faculty of the Graduate School 
of Cornell University for the degree of 

DOCTOR OF PHILOSOPHY 



BY 

VERN BONHAM STEWART 



[Reprint of Cornell Agricultural Experiment Station Bulletin 329, April, 1913] 



THE FIRE BLIGHT DISEASE IN NURSERY STOCK 



A THESIS 

Presented to the Faculty of the Graduate School 
of Cornell University for the degree of 

DOCTOR OF PHILOSOPHY 



BY 

VERN BONHAM STEWART 



[Reprint of Cornell Agricultural Experiment Station Bulletin 329, April, 1913] 






CONTENTS 



PAGE 

Host plants 317 

Species and varieties affected 317 

Economic importance of the nursery industry 317 

The disease 318 

History 318 

Names 318 

Occurrence 318 

Epidemics 319 

Theories as to cause 319 

Geographical distribution 321 

Economic importance 321 

Symptoms 321 

Blossom blight 322 

Twig blight 322 

Body blight 323 

Winter injury versus fire blight 323 

Etiology 325 

Name of parasite 325 

Description of Bacillus amylivorus 326 

Life history 338 

The cycle 338 

Disseminating agents 339 

Dissemination by pruning tools 342 

Special orchard considerations 344 

Hold-over blight 345 

Influence of weather on blight . . . .' 346 

Cultivation and manuring as affecting fire blight 347 

Varietal susceptibility 350 

Special inoculation experiments 354 

Pathological histology 356 

Control 3 6 i 

Tree-feeding 3 62 

Spraying 3& 2 

Patent nostrums 363 

General plan of control 363 

Control in nursery stock 364 

Inspection 3 $4 

Destruction of insect agents 368 

Bibliography 3^8 



JMN 1 1913 



316 



THE FIRE BLIGHT DISEASE IN NURSERY STOCK* 

V. B. Stewart 
HOST PLANTS 

SPECIES AND VARIETIES AFFECTED 

Fire blight is undoubtedly a native disease of the American indigenous 
species of Pomeae. It is known to affect the pear, quince, apple, apricot, 
plum, species of Crataegus, Amelanchier canadensis, Pyrus americana, and 
a few of the native species of the apple family. Waite ('07) reports its 
occurrence on the evergreen Eriobotrya japonica, and states that this 
species is somewhat commonly attacked by the disease in Florida, Georgia, 
and California. He has also observed the blight affecting the red-berried 
California holly {Heteromeles arbutifolia Roem.) in various parts of Cali- 
fornia, where this native species of Pomeae occurs in the vicinity of 
cultivated orchards. 

The disease is most destructive on the cultivated varieties of the pear 
{Pyrus communis), the apple {Pyrus malus), and the quince {Cydonia 
vulgaris). Intensive cultivation and artificial propagation have evidently 
tended to reduce the resistance to the blight in these plants. As a rule 
the pear and the quince suffer most, although the apple is often seriously 
injured and may be killed. This is particularly true of nursery stock 
and young orchard trees. Plums are seldom affected, but Jones ('02) 
found that the disease occurs on and kills the twigs of the Cheney plum 
{Primus americana nigra). Paddock ('03) reports the same disease 
occurring on the fruit and twigs of the apricot. The cherry and the 
peach are not known to be attacked. 

ECONOMIC IMPORTANCE OF THE NURSERY INDUSTRY 

Although the nursery business is a somewhat specialized industry, it 
is, nevertheless, of considerable economic importance. The figures re- 
cently published in this connection by the Department of Statistics of 
the Bureau of the Census ('12) are of special interest. Within recent 
years the nursery business of the country has shown a rapid increase. 

* Also presented to the Faculty of the Graduate School of Cornell University, January 27, 1913, 
as a major thesis in partial fulfillment of the requirements .for the degree of Doctor of Philosophy. 

Author's acknowledgments. — The writer" is •. fnSeBted tb Professors H. H. Whetzel and Dona'd 
Reddick, under whose immediate direction the work was conducted, for helpful criticisms and sugges- 
tions. 

('02) Jones, L. R. Studies on plum blight. Centbl. Bakt. u. Par. 2, 9 : 835-841. 1902. 

('03) Paddock, Wendall. An apricot blight. Colorado Agr. Exp. Sta. Bui. 84 : 5-14. 1903. 

('07) Waite, M. B. A new native host for pear blight. Science n. s. 25 : 286-287. 1907. 

('12) Press Notice, Department of Statistics of the Bureau of the Census. June 25, 1912. 

317 



318 Bulletin 329 

The total value of nursery products reported from 5,582 establishments 
in 1909 was $21,051,000; this was an increase of 591 establishments, or 
1 1.8 per cent, and $10,927,000, or 107.9 P er cent, in ten years. In 1909 
the Middle Atlantic division ranked first, with products valued at 
$4,355,000 as compared with $2,523,000 in 1899 — an increase of 
$1,832,000, or 72.6 per cent, during the decade from 1899 to 1909. Although 
the number of establishments reporting nursery products was greatest in 
the East North Central division, being 1,159, this division ranked fourth 
in value of products, being exceeded by the Middle Atlantic, West North 
Central, and Pacific divisions. In percentage of increase the Pacific 
division ranked first, with 377 per cent; the West South Central division 
second, 179.4 per cent; and the South Atlantic division third, 11 7.4 per 
cent. 

The three States ranking highest in value of nursery products in 1909 
were: New York, $2,751,000; California, $2,213,000; and Texas, $1,253,000. 
The standing in 1899 was, New York, Iowa, Illinois. An increase in 
value of nursery products was reported from all States except Maine, 
Vermont, Virginia, and South Carolina; and also excluding the District 
of Columbia. In the State of Washington the value of products in 1909 
was almost twenty times as great as that in 1899. 

THE DISEASE 

HISTORY 

Names 
The disease has been a theme for incessant discussion by horticulturists 
since the earliest days of fruit culture in this country. Various common 
names have been applied to the disease, depending to some extent on 
the host that is attacked and on the effect produced. Among the names 
most frequently used are fire blight, pear blight, blight, blossom blight, 
twig blight, fruit blight, sun scald, canker, and blight canker. The term 
" fire blight " is preferable, since it applies equally well to the character- 
istic symptoms of the malady on any of the different hosts. 

Occurrence 
Occurring as a disease of the indigenous wild crab-apple and hawthorn 
of eastern North America, the blight spread readily to orchards of pome 
fruits when the cultivated varieties were introduced into this country. 
It was first observed about 1780 in the Hudson River Highlands of New 
York State by William Denning (1794), an orchardist of that section. 

(1794) Denning, William. On the decay of appie trees. Trans. New York Soc. Prom. Agr. Arts and 
Manlr. I 2 : 219-222. 1794. [Second edition I 2 : 185-187. 1801.] 



The Fire Blight Disease in Nursery Stock 319 

Later, with the increase of the orchard industry, the disease became 
more prevalent aad gradually worked its way westward, as the plantings 
followed the settlement of the country beyond the Allegheny Mountains. 

Epidemics 

It was early maintained that the malady was more or less periodic 
in its occurrence, the periods of time being placed at five, ten, or twenty 
years. A careful examination of the literature of the subject gives little 
support to these views, but indicates that the lapse of time between 
epidemics of the disease has been irregular and has often varied for dif- 
ferent sections of the country. 

The years 1826 and 1832 were notable for increased prevalence of the 
malady, and one of the most widespread and destructive epidemics is 
recorded by Beecher (1844) as having occurred in 1844. Few orchards 
escaped without partial or total loss of many trees and some orchards 
were completely ruined. Since that time epidemics have occurred in 
different sections of the country, among which might be mentioned the 
serious outbreak of the disease about i860 in Massachusetts and border- 
ing States, as recorded by Cooke (1867). 

The most important epidemic of recent years was the appearance of 
the blight for the first time beyond the Rocky Mountains, reported by 
Pierce ('02) as having occurred in the pear orchards of California in 1902. 
In this and the succeeding two years it is reported by Smith (06) to have 
wrought such havoc as has seldom been known. 

Theories as to cause 

The disease being so common, various theories were enunciated, natur- 
ally, as to the cause, it generally being regarded as resulting from several 
factors either acting together or brought about by dissimilar circumstances. 

Action of sun. — Coxe (181 7) in his horticultural book, which is said 
to be the oldest publication on fruit culture in this country, was one of 
the first to advance an hypothesis. He ascribed the cause of the disease 
to the hot rays of the sun, and admirably characterized the symptoms 
of this in the following words: " That species of blight which is some- 
times called fire blight, frequently destroys trees in the fullest apparent 
vigor and health, in a few hours, turning the leaves suddenly brown as 
if they had passed through a hot flame, and causing a morbid matter to 
exude from the pores of the bark of a black ferruginous appearance. 

(1817) Coxe, William. Cultivation of fruit trees. Pear blight, 175-176. 1817. 

(1844) Beecher, H. W. The blight in the pear tree: L its cause and a remedy for it. Mag. Hort. 
10: 441-456. 1844. 

(1867) Cooke, S. S. Pear blight. Gardeners Monthly 9 : 73-78. 1867. 

('02) Pierce, Newton B. Pear blight in California. Science n. s. 16 : 193-194. 1902. 

('06) Waite, M. B., and Smith, R. E. Pear blight. Ann. Rept. California Fruit Growers Assoc. 31 : 
137-161. 1906. 



320 Bulletin 329 

This happens through the whole course of the warm season, more fre- 
quently in weather both hot and moist." ' 

Insects. — The ambrosia beetle, Xyleborns dispar Fabrieius (Scolytus 
pyri Peck), was also believed to be the cause, and among the prominent 
supporters of this view was Patrick Barry (1847), a pioneer nurseryman 
of New York State. 

Frozen sap. — The next hypothesis that attracted general attention was 
known as the " frozen sap theory," and was first promulgated by Reverend 
H. W. Beecher (1844). About this time we find the only mention of 
the disease with reference to nursery stock until the publications of more 
recent years. Gookins (1846), Ernst (1848), and James (1849) give 
brief mention of its occurrence in nursery trees. 

Fungus theory. — The fungus theory of the cause of fire blight was 
advanced by Dr. J. H. Salisbury (1863), and twelve years later Dr. J. G. 
Hunt (1875) thought he confirmed the opinion that it was due to a fungus. 

Electricity. — Electricity was believed by some investigators to be the 
cause of the blight, since diseased trees were often particularly noticeable 
after a thunderstorm. 

Bacteria. — The last hypothesis of historical importance is the bacteria 
theory, advanced by Professor T. J. Burrill (1879), a pioneer pathologist 
of this country. In 1878, after the blight had been known for nearly 
a century, Professor Burrill distinctly stated that he believed the cause 
to be due to bacteria which he found occurring in great abundance in 
the tissues of diseased branches. Three years later he reported (1881) 
the results of his inoculation experiments, whereby he caused healthy 
pear twigs to blight by inoculating them with the juices of diseased ones. 

Later, Arthur (1885) confirmed the results of Dr. Burrill and extended the 
cultural and inoculation experiments. His work proved absolutely that the 
malady is caused by bacteria. Since that time there have been a number of 
contributions to the knowledge of this disease, among which are to be men- 
tioned the work of Waite (1898), Jones ('02), Whetzel ('06), and Jones ('09). 

(1844) Beecher, H. W. The blight in the pear tree: its cause and a remedy for it. Mag. Hort. 10 : 441- 
456. 1844. 

(1846) Gookins, S. B., and Downing, A. J. Remarks on pear blight of the West. Hort. 1 : 253-256. 
1846. 

(1847) Barry, Patrick. Insect blight. Genesee Farmer 8 : 218. 1847. 

(1848) Ernst, A. H., and Downing, A. J. Fire blight in pear trees. Hort. 2 : 328-332. 1848. 

(1849) James, J. H. Blight in pear trees. Mag. Hort. 15 : 13-23. 1849. 

(1863) Salisbury, J. H. Pear, apple, and peach trees affected with blight. Ohio Agr. Rept. 1863 : 450- 
460, 469. 1864. 

(1875) Meehan, Thomas, and Hunt, J. G. Pear blight. Gardeners Monthly 17 : 245. i87S- 

(1879) Burrill, T. J. Fire blight. Trans. Illinois State Hort. Soc. 12 : 77-81. 1S79. 

(1881) Burrill, T. J. Anthrax of fruit trees: or the so-called fire blight of pear and twig blight of apple 
trees. Proc. Amer. Assoc. Adv. Sci. 29 : 583-597. 1881. 

(1885) Arthur, J. C. Proof that bacteria are the direct cause of the disease in trees known as pear 
blight. Proc. Amer. Assoc. Adv. Sci: 34 : 295-298. 1885. 

(1898) Waite, M. B." Life history and characteristics of the pear blight germ. Proc. Amer. Assoc. 
Adv. Sci. 47 : 427-428. 1898. 

('02) Jones, L. R. Studies on plum blight. Centbl. Bakt. u. Par. 2, 9 : 835-841. 1902. 

('06) Whetzel, H. H. The blight canker of apple trees. New York (Cornell) Agr. Exp. Sta. Bui. 
236 : 104-138. 1906. 

('09) Jones, D. H. Bacterial blight of apple, pear, and quince trees. Ontario Agr. Col. Bui. 176 : 1-63. 
1909. 



The Fire Blight Disease in Nursery Stock 321 

geographical distribution 

The disease occurs throughout the United States and Canada in practi- 
cally every section where pomaceous fruits are grown. No authentic 
records have ever been made of its occurrence in Europe or on any of 
the other continents. Its restriction to this country may be attributed, 
no doubt, to the fact that the quantity of stock of pomaceous fruits ex- 
ported from America is comparatively small, thus eliminating to a con- 
siderable extent the possibility of the disease being transported across 
the ocean. 

Fire blight is common in all the nursery districts of New York State 
and has frequently been destructive in the plantings of the Southern 
States, especially Alabama, Florida, and Georgia. It is a well-known 
malady in the nurseries of the Central and Middle West and has been 
reported by Orton ('02) as being especially abundant in Texas and 
Louisiana. The disease is somewhat generally distributed over the 
pear- growing section of the Pacific Coast, particularly in California and 
Oregon. 

ECONOMIC IMPORTANCE 

Without question, fire blight is the most important disease affecting 
the pomaceous fruits. Being of an epidemic nature, it may suddenly 
appear in a locality with increased prevalence and cause complete de- 
struction or severe injury to the fruit-tree industry of that section. Pear 
orchards, especially, are severely attacked, and often an orchard is entirely 
destroyed in one season. Although the blight may have subsided as an 
epidemic, it is usually found to a limited extent in any locality and under 
conditions favorable for its development and propagation it again be- 
comes a destructive disease. Usually, in the nursery it means total loss 
to the trees affected, and with its rapid spread through the blocks where 
the trees are thickly planted, often within a comparatively short time, 
thousands of young trees are ruined. In some cases entire blocks of 
apples, pears, and quinces have been destroyed. Such a condition pre- 
vailed in one of the nursery districts of New York State in 1908, and 
practically every nurseryman in that section suffered heavy losses from 
the disease. 

SYMPTOMS 

The limbs, blossoms, twigs, and fruit may be attacked. In the nursery 
the disease is most commonly found affecting the twigs, one exception 
being the two- and three-years-old quince stock. These trees often blossom 
profusely in the spring, and under this condition blossom blight fre- 
quently occurs. 

('02) Orton, W. A. Plant diseases in the United States in 1901. Pear blight. U. S. Dept. Agr. Year- 
book 1901 : 669. 1902. 



3 22 



Bulletin 329 



Blossom blight 
Sometime m the early part of the season, about two or three weeks 
after the blossoming period, the blight first attracts special attention 

and by a close examination the 
blighted blossoms may be detected 
even somewhat earlier. The first 
evidence of the trouble is the 
brown and subsequent blackened 
appearance of the young leaf tufts 
and the blossoms, from which the 
disease rapidly extends into the 
fruit spurs (Fig. 112). It prevents 
the development of the fruit and 
may even involve the larger twigs 
and branches. 



Twig blight 
The wilted and brown or dead 
appearance of the stem and foliage 
is the characteristic 
symptom of twig 
blight (Fig. 113) 
The progress of the 
disease down the 
stem, in the early 




Fig. 112. — Blossom blight 



stages, may be in advance of any 
marked discoloration of the foliage, 
and to a considerable degree the 
blighted twigs resemble green brush 
that has been only partially burned. 
There is generally a viscid, milk-white 
substance exuding in small drops 
on the surface of the twig or the 
petioles, which later becomes oxidized 
into an amber-yellow or slightly 
brownish, then finally into a dark 
brown or almost black, gum. 

The extent of the disease in advance 
of any discoloration of the foliage may 
be determined by the sappy and juicy 
appearance of the tissue. A faint amber-yellow or reddish discoloration 
of the tip is often a means of detecting recently affected apple shoots. 




Fig. 113. — Twig blight 



The Fire Blight Disease in Nursery Stock 323 

In pear twigs an intensive blackening of the tissue is usually character- 
istic, even in early stages of the infection. However, in all host plants 
the blight ultimately produces the same effect — the leaves shrivel, turn 
browner black, and resemble foliage that has been killed by frost. One 
of the most striking symptoms of fire blight to be recognized is in the 
twig or limb with dead, brown or black leaves clinging to it, contrasting 
sharply with the dark green foliage in summer and the naked branches 
of the trees in winter. In no other disease of the pome fruits do the 
leaves cling so tenaciously to the dead twigs. 

Body blight 
The blight often works down the twigs or branches into the trunk of 
the tree and within a short time may extend into the roots, causing the 
destruction of the whole tree. While the disease is active in the trunk 
or the larger branches, the affected tissue is darker in color, often with 
a brownish or reddish tinge. The abundance of sap gives the bark a 
water-soaked, or occasionally a slightly raised and blistered, appearance. 
(The blisters have also been observed even in the smaller pear and quince 
twigs.) The characteristic exudation is common and, when the disease 
is especially active, it may be so abundant that it flows slowly down the 

side of the tree (Fig. 114)- . 

With unfavorable conditions — as, for example, at the termination of 
the growing season, when the plant tissues harden and there is a dimi- 
nution in the sap supply— the active progress of the blight becomes checked 
by natural causes. The diseased bark shrinks and subsides, resulting in 
a sharp line of demarcation between the healthy and the diseased tissues. 

When only a definite area is affected, the diseased part surrounded by 
healthy bark is known as a canker (Fig. 115). The inner tissue of the 
diseased bark appears brown or dead, making a distinct contrast with 
the pale green or white, healthy tissue. In many cases the blight may 
still be present in a latent form cr may remain throughout the winter 
in apparently nondiseased tissue. With favorable conditions the follow- 
ing spring it again becomes active and progresses farther into the adjoining 
healthy bark. Hold-over cankers, in which the blight remains in a latent 
form throughout the dormant season, are rather common. 

WINTER INJURY VERSUS FIRE BLIGHT 

Diverse weather conditions during the dormant season may cause 
severe injury to the fruit stock in the nursery and frequently such injury 
is confused with fire blight. The results of winterkilling are usually 
manifest early in the spring by the injury to the trunks of the trees. 



3 2 4 



Bulletin 329 



There occur large cankered areas, which may completely girdle the tree 
and partially interfere with, or totally inhibit, the development of the 
new growth. If the injury has not been too severe some new growth 










PI 




Fig. 114. — Cankered limb, showing exuding milky drops 



may be made; but for lack of nourishment the young shoots soon wilt, 
turn brown, and die within a very short time, their condition thus 
resembling that brought about by fire blight. On the other hand, winter- 
killed trees show a uniform browning or dying of all the foliage; while 
with fire blight, in the early stages the dead discoloration is from the tip 



The Fire Blight Disease in Nursery Stock 



S25 




downward as the disease progresses toward the main part of the tree. 
The shoots of winterkilled trees appear wilted and dried out, due to in- 
adequate food supply, and there is no gummy exudation nor water- soaked 
appearance which is so common with 
blighted twigs.* 

ETIOLOGY 

Name of parasite 
The disease is caused by the 
bacterial parasite Bacillus amylivorus 
(Burrill) Trev. The organism was 
first described by Dr. T. J. Burrill 
(1883) and named Micrococcus 
amylivorus, the description of which 
is reproduced here: 

New Species of Micrococcus (Bacteria) — 
Micrococcus amylivorus. Cells, oval, single 
or united in pairs, rarely in fours, never 
in elongated chains, imbedded in an abun- 
dant mucilage which is very soluble in 
water; movements oscillatory; length of 
a separate cell .00004 to .000056 inch; width 
.000028 inch; length of a pair .00008 inch; 
of four united, about .00012 inch. 

In the tissues of plants causing the so- 
called " fire blight " of the tree and similar 

phenomena in many other plants. Through the action of the organism the stored 
starch is destroyed by fermentation and carbonic acid and hydrogen is given off 
(American Association for the Advancement of Science, 1880; Tenth Report Illinois 
Industrial University, 1880). 

The species was at first referred to the genus Bacterium, but this came from too 
exclusive attention having been given to its shape. It is only found in tissues of 
affected plants or oozing from their cells and smearing the surface. It may, however, 
be cultivated in pure starch in water maintained at the temperature of ordinary summer 
weather. No doubt other nutritive ingredients would make the culture easier and more 
prompt. 

The only recent system of classification of bacteria available at that 
time was that of Cohn (1872). Apparently Burrill placed considerable 
weight on the property of motility, and the fact that he did not observe 
this phenomenon in the fire blight organism (movements oscillatory) 
led him eventually to place it under the genus Micrococcus with the 
statement, " This species was at first referred to the genus Bacterium, 
but this came from too exclusive attention having been given to its shape." 
In the arrangement of Schizomycetaceae by De Toni and Trevisan in 

* It has been the experience of the writer that in blocks of two- and three-years-old apple and quince 
trees, when an abundance of iboth fire blight and winter injury is apparent, winter-injured trees seldom, 
if ever, blight. 

(1872) Cohn, Ferdinand. Untersuchungen iiber Bacterien. Biologie der Pflanzen I 2 : 127-224. pi. 3. 
1872. 

(1883) Burrill, T. J. New species of Micrococcus (Bacteria). Amer. Nat. 17 : 319. 1883. 



Fig. 115.— Canker on limb of tree 



326 Bulletin 329 

Saccardo's Sylloge (1889), the species is transferred (page 984) to the 
genus Bacillus with a reference to Trevisan (1889). An attempt has 
been made to see this pamphlet by Trevisan but all efforts to locate it in 
libraries of the United States have thus far been fruitless. It seems 
reasonably certain, however, that the rearrangement was made by 
Trevisan, not by De Toni as is sometimes stated. 

The specific name amylivorus as originally proposed by Burrill has not 
been adopted by any other worker. The term amylivorus does not seem 
to be orthographically incorrect, and in conformity with the Vienna code 
of botanical nomenclature the writer has employed Burrill's name. It 
should be noted in this connection that Saccardo's reference to " Mit- 
teilungen der (Esterreichischen Versuchs-Station fiirBrauereiund Malzerei 
in Wien" as the place of original description is incorrect. Burrill's 
description is brief, but there can be no question whatever regarding 
the organism that he saw and described. 

Description of Bacillus amylivorus 

Several descriptions of Bacillus amylivorus based on cultural characters 
have appeared thus far in literature. Most of them, however, are incom- 
plete and in several instances the various authors disagree concerning 
certain reactions of the organism. 

The first cultural studies on the organism were made by Arthur (1887). 
He grew the bacteria in various kinds of broth or liquid media, and to a 
limited extent on solid media. Waite (1898) published a brief and con- 
densed description of the characters in his article on the life history of 
the organism. The next description to appear is that of Chester ('01), 
based on the study of a single pure culture of the causal organism from 
a diseased pear twig. The organism was grown in but a relatively small 
number of kinds of media, and the reactions recorded differ strikingly 
from those obtained by L. R. Jones ('02). The work of Jones was based 
on a study of the bacillus from blighted twigs of both pear and plum, 
carried in parallel series through many kinds of media. Whetzel ('06) 
also reports some cultural work with the fire blight organism, and the 
results obtained apparently agree in general with the work of Jones. 
D. H. Jones ('09) of the Ontario Agricultural College has published the 



(1887) Arthur, J. C. History and biology of pear blight. Proc. Philadelphia Acad. Nat. Sci. 38 : 322- 
341. 1887. 

(i88g) Saccardo, P. A. Sylloge Fungorum 8 : 923-1087. 1889. 

(1889) Trevisan di Saint-Leon, Vittore. I generi e le specie delle batteriaceae; prodromo sinottico. 
Milano. 1889 : 1-36. 1889. 

(1898) Waite, M. B. Life history and characteristics of the pear blight germ. Proc. Amer. Assoc. 
Adv Sci. 47 : 427-428. 1898. 

('01) Chester, F. D. Notes on pear blight. Ann. Rept. Delaware Agr. Exp. Sta. 12 : 38-46. 1901. 

('02) Jones, L. R. Studies on plum blight. Centbl. Bakt. u. Par. 2, 9 : 835-841. 1902. 

('66) Whetzel, H. H. The blight canker of apple trees. New York (Cornell) Agr. Exp. Sta. Bui. 
236 : 104-138. 1906. 

('09) Jones, D. H. Bacterial blight of apple, pear, and quince trees. Ontario Agr. Col. Bui. 176 : 1-63. 
1909. 




The Fire Blight Disease in Nursery Stock 327 

first description of Bacillus amylivorus since the adoption of the chart 
by the Society of American Bacteriologists. 

For the cultural studies made by the writer, nine different cultures 
were used. Most of these were 
obtained from different sources 
in order to determine, if possible, 
any variations in the reactions 
as influenced by environmental 
conditions or by the period of 
time that the causal organism 
had been cultured artificially. 
For convenience each culture 
was designated as a different 
strain and, unless otherwise 
stated, all nine strains were 
included in each test. The 
source and number of each 
strain is as follows: 
No. 1 . Isolated from pear tree, 

October 10, 1909, Cornell Fig. 116. — Bacillus amylivorus, showing peri- 

campus, near old forcing- trichic flagella. Moore's modification of 

1 ° Loe ffler s jl a gel la stain 

house. 

No. 2. Obtained from Professor T. D. Beckwith, Oregon Agricultural 

College, November, 191 1. 
No. 3. From same tree on Cornell campus as No. 1. Isolated in 

November, 19 10. 
No. 4. From the same pear tree as numbers 1 and 3. Isolated in 

October, 191 1. 
No. 5. From Professor D. H. Jones, Guelph, Ontario, Canada. Isolated 

from apple tree. Received culture from him in October, 19 10. 
No. 6. Isolated from pear by Professor W. G. Sackett, Colorado Agricul- 
tural Experiment Station. Received culture from him in March, 191 1. 
No. 7. Isolated from small pear twig by Professor W. G. Sackett, 

April 21, 191 1. Colorado. 
No. 8. From two-years-old quince tree in nursery. Orleans, New York, 

June, 191 1. 
No. 9. From apple tree, West Hill, Ithaca, New York, October, 191 1. 

In general, the reactions in different media for all the strains were 
fairly uniform and no marked differences were noticed; the behavior of 
the organism in milk cultures showed the greatest variation. It should 
be noted that a strain from Colorado, No. 7, always made a slower growth 
than any of the others; while No. 9, recently isolated from apple at Ithaca, 



328 Bulletin 329 

New York, was usually the most rapid grower. Commonly the first 
indications of growth by No. 7 were not apparent until several hours after 
that of the other strains. When there were any differences in the reactions, 
Strain No. 8, from quince, was always taken as a basis for comparison. 
' Morphological characters. — Vegetative cells. The fire blight organism is 
a bacillus of slightly variable length, usually within the limits of .6 to .9 
by 1 to i.S^u. Short rods with rounded ends, mostly single, sometimes 
in twos and occasionally in chains of three or four. Taken directly from 
fresh gummy exudate of diseased quince twig and stained with alcoholic 
carbol fuschin, the single rods measured .6 to .8 by 1.4 to i.8ju- A two- 
days-old culture on agar when stained with carbol fuschin gave the 
measurements .7 to .8 by 1.5 to 1.7/*- Measurements of the same strain, 
No. 8, on agar cultures sixty days old were slightly less, .6 to .7 by 1.2 
to i-4M- When taken from a three-days-old culture of bouillon and 
stained with carbol fuschin, the limits of size were .7 to .9 by 1.6 to 
1.8/z. In general, the measurements in length of strain No. 7, from 
Colorado, were slightly less, the rods being somewhat shorter. Taken 
from six-days-old bouillon culture and stained with carbol fuschin, the 
size of rods was .7 to .8 by 1.2 to i-3/x- 

Endospores. No endospores have been observed. 

Flagella. The organism is motile by means of peritrichic flagella, 
usually two or three in number, stained by Moore's modification of 
Loeffler's flagella stain (Fig. 116). 

Capsules. None demonstrated. 

Zooglceae. None formed. In his work on the history and biology of 
pear blight, Arthur (1887) illustrates zooglceal formations. These were 
no doubt due to the presence of other organisms often found on the surface 
of diseased tissues, as was later pointed out by Miss Snyder (1898). 

Involution forms. None observed. 

Staining reactions. The organism stains readily with watery and 
alcoholic solutions of gentian violet, carbol fuschin, and methylene blue. 
Gram's stain, and also Ziehl-Neelson, proved negative. 

Cultural characters. — In the preparation of the culture media the direc- 
tions as given by Smith ('05) were followed as closely as possible. Dis- 
tilled water was used in preparing all media unless otherwise stated. 
The beef broth was made from minced lean beef and Witte's peptone. 
All media containing nutrient bouillon titrated +15, Fuller's scale, unless 
otherwise stated; N /2o sodium hydroxid was used for titrations, with 
phenolphthalein as an indicator. 



(1887) Arthur, J. C. History and biology of pear blight. Proc. Philadelphia Acad. Nat. Sci. 38 : 322- 
341- 1887. 

(1898) Snyder, Lillian. A bacteriological study of pear blight. Proc. Amer. Assoc. Adv. Sci. 47: 426- 
427. 1898. 

('05) Smith, E. F. Bacteria in relation to plant diseases I : 1-285. 1905. 



The Fire Blight Disease in Nursery Stock 329 

Agar colonies. Colonies appear on second day, characteristic on 
fifth day, at 23 C. When isolations are made from diseased tissue, the 
colonies appear on the second day at a temperature of 23 ° C, becoming 
characteristic on the fourth or fifth day. The surface colonies are usually 
small, not more than two to three millimeters in diameter. They have 
a somewhat shiny luster, and are smooth, white, flat or slightly raised, 
having a finely granular or cloudy circular growth, with a dense opaque, 
sharply defined, white center. The margin is entire or slightly undulate. 
Older colonies are coarsely granular to grumose. Deep colonies are 
globose, or more often lens-shaped, with dense opaque center. Plates 
poured from young beef -broth cultures show colonies developing usually 
after forty-eight hours. 

Agar stroke. Moderate growth, filiform, slightly raised, glistening, 
slightly gray. A moderate growth after twenty-four hours at 23 ° C, 
more characteristic, however, after forty-eight hours; filiform, has a glisten- 
ing luster, opalescent. The white streak does not branch on the surface 
nor penetrate the agar. The growth often widens, becoming more diffuse, 
spreading mainly toward the bottom where moisture is present on surface 
of agar. Often in isolated colonies or beaded above before becoming 
diffuse and spreading at bottom. Water of condensation at base of 
streak turbid and with flocci. Does not stain the agar on which it grows. 
It is free from odor. Slightly to considerably raised, more or less pul- 
vinate in cross-section, semi-opaque. 

Agar stab. Growth filiform, uniform, nontypical. Feeble growth after 
twenty-four hours at 23 C, most characteristic after forty-eight hours, 
filiform, best toward the top. Surface growth smooth, with general 
tendency to spread somewhat. Agar not liquefied nor softened. 

Nutrient gelatin colonies. Colonies are round, slightly raised, entire, 
grayish. In plates poured from a three-days-old beef bouillon culture 
the colonies were rather numerous but very small, appearing as tiny 
specks after three days. In the dilution plates the colonies were some- 
what larger; after the fifth day they appeared finely granular under low 
power of microscope and later became grumose. Liquefaction of gelatin 
very slow, only slightly evident after fifteen days. 

Gelatin stab. Growth moderate, slight liquefaction after fifteen days. 
Growth slow and feeble for the first two or .three days on +15 nutrient 
gelatin at 20 C. Slight tendency to be beaded or granular along lower 
line of platinum needle stab. After eight days moderate increase in 
growth, with indication of slight liquefaction after fifteen days. Crateri- 
form to stratiform. 

Sta±> cultures were made in tubes of nutrient gelatin with the following 
acidities: neutral, +10, +15. In these cultures, strains numbers 1, 7, and 



330 Bulletin 329 

8 were used. At a temperature of 23 ° C. there was a slight growth in 
all tubes after twenty-four hours, more marked, however, after three days. 
The most vigorous strain was No. 8, and there was considerable surface 
growth in this strain; while No. 7 showed the weakest development, with 
surface growth but slight. The +10 and +15 tubes were somewhat 
more favorable for the organism than was the neutral medium. Although 
the liquefaction in the acid cultures was only slight after fifteen days, it 
was still less in the neutral cultures. 

Potato plug. Growth moderate, nonviscid, glistening white, no odor, 
spreading. Growth generally appearing after forty-eight hours, not so 
rapid nor so abundant as on agar streak. Slightly elevated, glistening, 
moist, pearly white, slowly spreading over the surface of the potato, 
entire margin, not viscid. It is free from odor and turns the potato plug 
grayish, which later becomes darker in color. 

Loeffler's blood serum. Growth moderately slow, colorless, no lique- 
faction. Feeble growth after forty-eight hours, more characteristic after 
four days at 23 C. No branching of the white streak on the surface nor 
penetration of the medium. Slight tendency to spread at the base, 
slightly raised, sometimes beaded or in isolated colonies, glistening. 
Does not stain nor liquefy the serum. (Strain No. 1 was used for these 
studies.) 

Starch jelly.* Growth moderate, diastatic action absent or feeble, 
medium unstained or slightly stained. The experiment was repeated 
several times, but no marked changes as recorded by Jones ('09) were 
observed. One or two of the tubes showed a very slight liquefaction 
when left at 25 C. In the enzyme studies, subsequently discussed 
(under " Pathological histology "), tests were made for the production 
of diastase ; but the results were negative except in one or two cases, when 
a slight test for reduction of starch was obtained. 

Bouillon +15 with 1 per cent Witte's peptone. Cloudiness uniform, 
moderate, no pellicle, no ring, no odor. Tubes of +15 peptonized beef 
bouillon were inoculated from sixteen-days-old slant agar culture. After 
twenty-four hours at 23 ° C. there was a uniform clouding with flocci and 
slight sediment. After forty-eight hours, cloudiness increased, flocci 
abundant and more or less persistent. No pellicle formed and odor not 
marked. Culture fluid showed tendency to clear after seventeen days. 

Sugared peptone water. Growth very moderate with apparently no 
staining of the fluid, in flasks of sterilized lake water containing Witte's 
peptone, c. p. glucose, and Baker's c. p. calcium carbonate. 

Milk. Coagulation slow, extrusion of whey beginning only after 
several days. Partial to complete digestion of curd. Tubes of sterile 

* For composition see Smith, " Bacteria in relation to plant diseases " I : 196. 1905. 
('09) Jones, D. H. Bacterial blight of apple, pear, and quince trees. Ontario Agr. Col. Bui. 176 : 1-63. 
1909. 






The Fire Blight Disease in Nursery Stock 



33i 



milk titrating +8 with phenol phthalein were inoculated with a one- 
millimeter loop of a beef bouillon culture, two days old, and kept at 23 C. 
No apparent change was observed until after nine days, when there was 
a slight formation of whey as a shallow layer on the surface of the milk. 
After twenty days coagulation was more advanced. At the end of five 
weeks there was a tendency for partial to complete digestion of curd. 
No discoloration of coagulum. 

Litmus milk. Reduction of litmus slow. Tubes of sterile litmus 
milk were inoculated with a one-millimeter loop of a two-days-old beef 
broth culture and kept at 23° C. After ten days there was a very slight 
increase in the blue color. In twenty days the reduction of the litmus 
was apparent, with the formation of whey at the surface. Tubes after 
forty to fifty days showed a return of the neutral lavender color, with a 
slight change to red after sixty days. Coagulation slow, with partial 
to & complete peptonization of the curd which was wholly bleached. _ 

Although several tests were made with the growth of the organism 
in milk cultures, there was never any rapid separation and digestion of 
the coagulum such as Jones ('09) describes. The changes in the medium 
were always slow. 

The most constant and marked differences in growth of the various 
strains were also apparent in the milk cultures. The general tendency 
for all strains was a slow separation and digestion of the curd. However, 
as is to be noted in the table below, the completion of this process was 
more marked in some cases than in others. 

TABLE 1 Reaction of Strains of Bacillus amylivorus in Sterile, Lavender, 
Blue Litmus Milk at 23° C. 



Strain 



Ten days 



Slightly bluer than check . 
Slightly bluer than check. 
Slightly bluer than check . 
Slightly bluer than check . 



Sixty days 



Unchanged 

Bluer than check. 



Much bluer than check. . . 
Slightly bluer than check , 

Slightly bluer than check 



Complete digestion of curd, white bacterial 

precipitate in bottom, whey lavender to red 
Complete digestion of curd, white bacterial 

precipitate in bottom, whey rose purple 
Moderate digestion of curd, wholly bleached, 

whey reddish 
Partial to complete digestion of curd, whey 

reddish 
Moderate digestion of curd, whey rose purple 
Slight digestion of curd, wholly bleached, whey 

red 
Very slight digestion of curd, wholly bleached 
Partial to complete digestion of curd, whey 

lavender to red 
Partial to complete digestion of curd, whey 

red 



(•09) Jones, D. H. Bacterial blight of apple, pear, and quince trees. Ontario Agr. Col. Bui. 176: 1 63. 
1909. 



332 Bulletin 329 

Cohn's solution. No growth. 

Uschinsky's solution. Growth moderate, nat viscid. Tubes of Uschin- 
sky's solution were inoculated from a beef broth culture two days old. 
After twenty-four hours at 23 ° C. a scanty growth was apparent, slightly 
clouding the solution by the granular particles suspended in the liquid. 
At the end of four days the maximum growth was reached. The liquid 
was moderately cloudy; did not become fluorescent or viscid. There was 
no pellicle formed, but a slight sediment was apparent in the bottom of 
the tube. 

Sodium chlorid bouillon. Six per cent of sodium chlorid inhibits 
growth. Five per cent inhibits or retards growth. Transfers were made 
with a one-millimeter loop from a two-days-old, + 15, peptonized bouillon 
culture to +15 bouillon tubes containing 2, 3, 4, 5, and 6 per cent of 
c. p. sodium chlorid. At the end of two days there was a good growth 
in the tubes containing 2 and 3 per cent of sodium chlorid, but the growth 
in the 3- and 4-per-cent solutions was best after four days. There was 
a gradual retardation of growth up to 6 per cent of sodium chlorid, which 
inhibited the growth of the organism in practically all cases. Apparently 
5 per cent of sodium chlorid is about the limit for the development of 
the organism. Most recently isolated strains appeared least adapted to 
the high concentrations of the solution. 

Best media for long-continued growth. Cultures in litmus milk, milk, 
and bouillon and on agar stab, which had been growing for five months, 
showed growth when transferred to +15 bouillon. Cultures on potato 
and gelatin of the same age showed no growth. 

Growth in bouillon over chloroform. Growth inhibited. Transfers of 
a two-millimeter loop from a two-days-old, +15, peptonized bouillon 
culture were made to Erlenmeyer flasks containing 30 cubic centimeters 
of +15 peptonized bouillon. To each flask was added 15 cubic centi- 
meters of chloroform (Squibb 's). The tops of the flasks were covered 
with oil-paper in order to prevent evaporation. No growth occurred 
after ten days in any of the flasks. 

Quick tests for differentiation purposes. The following are perhaps 
the most satisfactory tests: agar colonies, agar stroke cultures, gelatin 
stab, behavior in Cohn's solution, growth on starch jelly and also in beef 
bouillon, inoculation into young succulent twigs of apple, pear, or quince 
trees. 

Fermentation tubes. No gas is produced and the organism is aerobic 
in its tendencies. A solution was made by adding 2 per cent of Witte's 
peptone to filtered lake water. From this, six solutions were then made, 
each containing 1 per cent, respectively, of one of the following carbon 
compounds: cane sugar, dextrose, glycerin, mannite, maltose, and 



The Fire Blight Disease in Nursery Stock 333 

lactose. Four fermentation tubes were filled with each of the solutions 
and sterilized in an Arnold steamer for twenty minutes, on three days m 
succession. Three tubes of each set were inoculated and one was left 
for control. The inoculations were made by transferring a one-milli- 
meter loop from a three-days-old, +15, peptonized beef bouillon culture. 
Three days after inoculation all tubes showed a slight cloudiness m the 
open ends of the tubes. After five days the cloudiness was more marked 
in the tubes containing dextrose, cane sugar, mannite, and maltose than 
in the glycerin and lactose. After eighteen days the cloudiness had 
extended slightly beyond the middle of the U in the dextrose, cane sugar, 
and mannite tubes, and in all solutions there was a distinct, moderately 
flocculate precipitate formed, with solid particles floating in the liquid. 
The precipitate in the glycerin and maltose was slightly less; however, 
the cloudiness extended to the bend in the tube. The least growth was 
obtained in the lactose solution; there was a moderate amount of pre- 
cipitate, which had a tendency to be stringy, and the cloudiness extended 
nearly to the middle of the U. 

There was but little variation in the appearance of the different strains 
of the organism grown in the above solutions, and tests made after nine- 
teen days with respect to the acidity of the different cultures gave uniform 
results for all the strains. Tests made with litmus gave the following 
reactions for the cultures in the different solutions, the increase in acidity 
being proportionate to the amount of growth in the various solutions: 

Lactose — strongly alkaline 

Glycerin — alkaline 

Maltose — alkaline 

Mannite — neutral to weakly acid 

Cane sugar — weakly acid 

Dextrose — strongly acid 

Another series of tubes gave the same tests after the cultures had been 
running fifteen days. 

Two-per-cent ammonium lactate and two-per-cent carbon compounds. 
Moderate growth with cane sugar and slight growth in the mannite 
solution. A solution was made by adding 2 per cent of c. p. ammonium 
lactate to filtered lake water. Six solutions were made, from cane 
sugar, dextrose, mannite maltose, glycerin, and lactose. The solutions 
were placed in test tubes and sterilized in an Arnold steamer for 
twenty minutes, on three days in succession. Inoculated tubes re- 
ceived a one-millimeter loop of peptonized beef bouillon culture, six days 
old. All nine strains were used and cultures were grown at a temperature 
of 23 C. After five days there was a faint cloudiness in the mannite 



334 Bulletin 329 

solution and a moderate growth occurred in all the tubes containing cane 
sugar. There was a moderate reduction of the cane sugar to glucose, and 
the cultures were slightly acid to litmus. No growth in any of the other 
solutions after fifteen days. Fermentation tube cultures made at the 
same time showed no gas production. 

Potassium nitrate and carbon compounds. Slight growth in tubes 
containing dextrose. Six solutions were made, containing 1 per cent 
c. p. potassium nitrate and distilled water plus one of the following carbon 
compounds: cane sugar, dextrose, mannite, maltose, glycerin, and 
lactose. Tubes of these solutions were inoculated with a one-millimeter 
loop from a five-days-old, +15, bouillon culture. 

A faint cloudiness was apparent in the dextrose solution tubes, but no 
growth occurred in any of the others after fifteen days. All dextrose 
tubes gave alkaline reaction with litmus. No gas production in fer- 
mentation tubes containing the above solutions. 

Two per cent asparagin. Slight to moderate growth. Sterile tubes of 
a 2-per-cent solution of asparagin and filtered lake water were inoculated 
with a one-millimeter loop from a three-days-old, +15, bouillon culture. 
A slight to moderate growth occurred after five days at 23 ° C. This 
would indicate that the organism is able to obtain both its nitrogen and 
its carbon from asparagin. 

Ammonia production. None produced. 

Nitrates. Nitrates are not reduced. Transfers of each of the nine 
strains were made to 10 cubic centimeters of +15 peptonized beef bouillon, 
to which had been added enough potassium nitrate to make a i-per-cent 
nitrate bouillon solution. After three days there was a distinct cloudy 
growth in the tubes, and tests were made for nitrites as follows: To the 
inoculated tubes that had grown for four days, 1 cubic centimeter of boiled 
starch water and 1 cubic centimeter of potassium iodide solution (1-200) 
were added, then there were added a few drops of strong sulfuric-acid 
water (2:1); but no blue color resulted, indicating that there was no 
formation of nitrites. Other tests made with various strains at different 
intervals always gave negative results for the presence of nitrites. 

Indol. None formed. The indol tests were made by using concen- 
trated sulfuric acid and dilute sodium nitrate (1-200 in water). Tests 
were made with all nine strains of the organism. Two-days-old pep- 
tonized beef bouillon cultures were tested, and also similar cultures eleven 
and twenty days old respectively. No trace of indol was detected in 
any of the cultures, even on heating to 8o° C. after the sulfuric acid and 
nitrate were added. 

Toleration of acids. Toleration of acids is slight. Transfers from 
a two-days-old, +15, bouillon culture were made to tubes of -f-8, +10, 



The Fire Blight Disease in Nursery Stock 335 

+ 12, +15, +16, +19, +20, +23, +25, and +27 peptonized beef 
bouillon.* After four days, growth was apparent in all tubes up to +23. 
No growth occurred in +23, +25, and +27. The addition of malic 
acid in small amounts to +10 beef bouillon favored a slight increase in 
growth. Increasing the acidity from +10 to +12 by malic acid appeared 
to favor the growth of the bacilli. No growth occurred in +15 peptonized 
beef broth acidified to +25 by addition of normal malic acid. 

Toleration of potassium hydroxid. Toleration of alkalies rather low. 
Tubes of bouillon titrated with phenolphthalein to —4.5, —5.5, —6.5, 
— 7, and — 8 were inoculated with a one-millimeter loop from a three- 
days-old, + 15, bouillon culture. At 23 C. after six days, growth occurred 
in all the tubes except the — 7 and the — 8. 

The experiment was repeated, and after four days there was a faint 
cloudiness in the — 4.5 tubes. Two days later slight growth was apparent 
in all tubes up to the — 7. In the — 7, strain No. 1 showed a slight cloudi- 
ness in three of the five tubes. An alkalinity of — 6 is about the limit 
for growth of the organism. 

Optimum reaction for growth in bouillon. The optimum reaction lies 
between +8 and +16 on Fuller's scale. From studies made on toler- 
ation of acids and alkalies, the optimum reaction appears to be between 
+ 8 and +16. The limits for growth in peptonized beef broth are between 
— 7 and +25, Fuller's scale. 

Temperature relations. — Thermal death-point. The death-point is 
about 47 C. Tests were made by exposing for ten minutes in +15 
peptonized beef bouillon. Preliminary tests indicated that the thermal 
death-point must lie between 43 ° and 49 C. Three different strains of 
the organism were used in these tests, numbers 1,7, and 8. The tubes of 
peptonized beef broth were inoculated with a one-millimeter loop of a 
two-days-old beef bouillon culture, and then placed in water at practi- 
cally constant temperatures of 46 , 47 , and 48 C, respectively. At the 
end of ten minutes the tubes were removed from the water bath and 
incubated at a temperature of 22 to 24 C. After four days, growth 
was apparent in the tubes subjected to the temperature of 46 C. No 
growth occurred in any of the others. The experiment was repeated 
three times with the same result, which indicates that the thermal death- 
point of this organism is about 47 C. No differences were noticed for 
any of the strains used. 

Optimum temperatures. Best growth between 22 and 25 C. 
Growth on +15 nutrient agar was much better at 23 ° C. than at 32 . 
A temperature of io° to 12 C. also retarded the growth of the 
organism. 

* The bouillon for these tests was made from Liebig's beef extract instead of from fresh minced beef. 



336 Bulletin 329 

Cultures in incubator. Transfers of strains numbers 1,7, and 8 were 
made to peptonized +15 bouillon from a two-days-old bouillon culture 
and immediately placed in the incubator at a temperature of 37 C. 
No growth appeared after twelve days. Check cultures made good 
growth at 23 ° C. 

Resistance to drying. Moderate resistance to drying. Tiny drops of 
a ten-days-old peptonized beef bouillon culture were transferred to sterile 
cover-glasses in a covered sterile petri-dish and allowed to dry in the 
dark at a temperature of 20 to 22 C. The covers were then taken up 
by means of sterile forceps and dropped into tubes of sterile bouillon, 
one to each tube, with the following results: number of days dried, 1, 2, 
3, 4, 5, all cultures were alive and gave good growth in the bouillon tubes. 
The experiment was repeated, using a two-days-old peptone bouillon 
culture. The drops were about the same size as in the previous tests. 
Covers were kept in the dark. Results as follows; first tests made after 
six days drying: 

6 days — 4 tubes — all good growth 

7 days — '- 2 tubes — all good growth 
9 days — 2 tubes — no growth 

1 2 days — 2 tubes — no growth 
14 days — 2 tubes — no growth 

Minimum temperature. Organism resistant to prolonged freezing. 

Freshly poured agar plates were made from a six-days-old peptonized 
beef bouillon culture of strain No. 8. The plates were wrapped in paper 
and immediately placed in a tin can, which was imbedded in an ice-salt 
mixture contained in a granite pail. The temperature obtained by means 
of the mixture varied from — 14 to — 16 C. Two plates were removed 
at each of the following intervals: three hours, four and one half hours, 
seven hours, twenty-three hours; and in each case the plates were im- 
mediately placed in the incubator at a temperature of 23 C. Colonies 
developed in abundance in all the plates. Plates subjected to the freezing 
temperature for twenty-three hours showed' some retardation; however, 
there was practically no decrease in number of colonies that developed. 
On February 3, 191 2, three bouillon tubes and three agar slant tubes 
freshly inoculated from an agar slant culture of strain No. 8 were placed 
in a quinine can containing a mixture of pulverized ice and salt. The 
can, being provided with holes in the bottom in order to allow the escape 
of water from the melting ice, was placed in a granite pail. The freezing 
apparatus was kept out of doors and the temperature of the mixture 
was recorded three times a day. The cultures were re-iced twice each 
day, a new supply of salt (about three tablespoonfuls) also being added 



The Fire Blight Disease in Nursery Stock 337 

each time. The average temperature was about — 14 C. ; owing to 
extreme cold weather, however, it was as low as — 2 8° C. on one or two 
occasions. 

After five days of constant freezing, one agar and one bouillon tube 
were removed. A very slight growth was apparent on the agar slant, 
and on melting the bouillon it showed a faint cloudiness. The tubes 
were placed in the incubator at a temperature of 23 ° C, and after eighteen 
hours agar plates were poured in which developed the characteristic 
fire blight colonies. On the eleventh day of freezing two more tubes 
were removed and placed in the incubator. After thirty-six hours, growth 
was apparent in both the agar and the bouillon tubes. The last two 
tubes were removed from the freezing mixture on the fourteenth day and 
they gave good growth after thirty-six hours at 23 C. 

Effect of sunlight. — Freshly poured agar plates were exposed on ice to 
direct sunlight after covering a part of each plate with heavy pasteboard. 
Plates exposed for one hour showed several colonies developing after 
four days incubation at 23 C. Plates exposed for four hours and then 
incubated at about 23 ° C. gave no growth in the unprotected parts. 
The temperature of the agar throughout the exposure was between 23 ° 
and 26 C. 

Ferments. — Invertase. The different strains of the organism were 
grown for nineteen days in sterilized filtered pond water containing 2 
per cent of Witte's peptone and 1 per cent of c. p. cane sugar. 

Tests were made for glucose with Fehling's solution. All tubes showed 
considerable reduction, being the strongest in cultures of strains numbers 
2, 5, 7, and 8. The checks gave a negative test for glucose. It is to be 
inferred from these tests that a moderate amount of the invertase fer- 
ment is produced. 

Crystals. — Silky, needle-like crystals were formed in old litmus-milk 
cultures. The washed crystals were sparingly soluble in water; and 
when this aqueous solution was mixed with a solution of mercuric nitrate 
a yellow precipitate was produced, which, when boiled with dilute nitric 
acid, acquired an intense red color. This reaction is used as a test for 
tyrosine. The crystals were also tested with Mormer's reagent (1 volume 
formaldehyde, 45 volumes distilled water, and 55 volumes concentrated 
sulfuric acid), which gives a green color with aqueous solution of tyrosine. 

Germicides. — Poured agar plates were made with strain No. 8 of the 
organism after exposure to various concentrations of copper sulfate, 
mercuric chlorid, and formaldehyde solution. 

Poured plate cultures showed growth after three days when exposed 
for ten minutes to copper sulfate 1:10,000; no growth occurred when 
exposed for fifteen and twenty minutes to the same strength. No growth 



338 Bulletin 329 

in poured plate culture after ten and twenty minutes exposure to mer- 
curic chlorid 1 : 20,000. Plate cultures showed growth after three days 
when exposed for ten and twenty minutes to formalin 1 : 750, also 1 : 1,000. 
Growth occurred after ten minutes exposure to formalin 1 : 500, but 
none after twenty minutes. Checks gave good growth in all cases. 

Pathogenicity.— The organism is pathogenic to many species of genera 
in the tribes Pomeae and Pruneae of the Rosaceae family. 

Loss of virulence— In cultures carried for several months there was 
a slight loss of virulence as compared with cultures recently isolated. 
But little difference could be noticed in cultures that had been carried 
for one year and three years, respectively. 

Group number. — The group number, according to the descriptive chart 
of the Society of American Bacteriologists, is 211.2322033. 

LIFE HISTORY 

The cycle 

Following the work of Burrill and Arthur, subsequent investigations 
were concerned more with the question of the life cycle of the organism 
and the conditions under which blight occurs. Waite (1898) has con- 
tributed the most to our knowledge of the life history of the germ and 
advanced the first authentic evidence as to how blossom and twig blight 
are brought about. He proved that insects, such as flies and bees, carry 
the bacteria from oozing cankers to opening blossoms and from there 
to other trees, spreading the bacteria to the blossoms. More recently 
the observations of other investigators tend to show that a number of 
other insects are responsible agents in spreading the disease. The bacteria 
are probably not blown by the wind, as they are contained in a sticky 
gum. It would be practically impossible for them to be carried in this 
manner. Furthermore, Waite has shown that the probability of 
infection being produced in this way is very small, since a consider- 
able mass of the organism is required in order to produce infection. 

As previously stated, the bacteria that remain alive throughout the 
winter in " hold-over " cankers become virulent with the ascent of sap 
and the increased temperature of spring. They multiply and spread into 
the adjoining healthy bark. Often, when their increase is augmented by 
warm, rainy weather, the gummy exudation, laden with bacteria, oozes 
out of the lenticles and cracks of the infected tissue. This exudation, 
containing millons of the minute bacteria, usually takes place first about 
the time when the blossoms are opening. Various insects, such as wasps, 
honeybees, and flies, are attracted to these hold-over cankers by the 

(1808) Waite, M. B. Life history and characteristics of the pear blight germ. Proc. Amer. Assoc. 
Adv. Sci. 47 : 427-428. 1898. 



The Fire Blight Disease in Nursery Stock 



339 



sweet, gummy exudate, become smeared with it, and carry the infection 
material to the blossoms. Here some of the bacteria brought by the 
infected insect are left in the nectar of the flower. The sweet solution 
greatly favors their increase in 
numbers, and the next bee or other 
insect carries the organism to all 
the succeeding blossoms that are 
visited. 

After the parasite has established 
itself in the nectary of the blossom, 
the tissues of the flower soon be- 
come diseased and within a short 
time the characteristic symptoms 
of blossom blight are apparent. 
After the blossoming period, or 
sometimes even before it is entirely 
over, the blight may appear in the 
young succulent shoots, or twigs. 
Ordinarily in the nursery, where 
blossoms are not common except 
in the two- and three-years-old 
quince stock, the first occurrence 
of the blight in spring is in the 
twigs. However, instances have 
been observed when the disease 
first appeared in the quince blossoms 




Fig. 



117. — Blighted shoots. Infection 
occurred at base of petiole 



and was later spread to the succulent shoots. Not only do the new 
infections occur throughout the summer, but the disease continues to 
spread in an aifected tree and, unless checked in some manner, may 
involve the entire tree. Infections usually occur through the tips of the 
shoots, but the bacteria are frequently introduced into the tissues at the 
base of a petiole (Fig. 117). 

Disseminating agents 
Such agents as bees and wasps have been conceded, largely on evidence 
presented by Waite (1898), to be important in the spread of blossom 
blight. In recent years certain other insects have been associated with 
abundant twig infections. It has been definitely proved that the aphids 
(Aphis pomiDeGeer) spread the disease (page34i),andobservations during 
the past two seasons indicate that several other sucking insects may dis- 
seminate the blight bacteria in the nursery. On July 1, 191 2, the following 

(1898) Waite, M. B. Life history and characteristics of the pear blight germ. Proc. Amer. Assoc. 
Adv. Sci. 47 : 427-428. 189S. 



340 Bulletin 329 

species of sucking bugs were collected from apple nursery stock by Pro- 
fessor C. R. Crosby of the Department of Entomology, Cornell University: 
Reduviolus jerus Linn., Plagiognathus politus Uhler, Platymetopius acutus 
Say., Empoasca malt Le Baron, Typhlocyba rosae Linn., Compylomma 
verbasci Meyers, and Lygus pratensis Linn. 

It has not as yet been definitely determined that these species do spread 
the disease, but a large percentage of them are undoubtedly active agents 
in disseminating the blight bacteria. Visiting blighted tissues, the 
insect becomes smeared with the gummy exudate and carries the bacteria 
to the tender twigs; here, in sucking the sap, the insect punctures the 
tissues, thus forming a means of entrance for the blight germs, with the 
result that the twigs may soon become infected. 

Tarnished plant bug. — It is believed that one of the most important 
agents in transmitting the blight parasite to healthy trees, for the last 
two seasons at least, has been the tarnished plant bug {Lygus pratensis 
Linn.). This insect has been recognized for many years as causing severe 
injury to peach stock, but until recently it has never been considered 
a serious pest to other nursery trees. Due to the stinging of the terminal 
shoot of first-year peach buds, there is a tendency for the trees to make 
a stunted, bushy growth, thus failing to reach the proper height. Not 
only has peach stock been injured in this way, but also considerable 
damage was apparent during the season of 191 1 in several blocks of 
first-year apple buds. 

The same trouble was again noticed in 191 2, and a large number of 
apple shoots that had been stung by the insect a few days previous de- 
veloped infections of fire blight. Apparently this tarnished bug was 
responsible for the infections that occurred. Being abundant also in 
blocks of two-years-old apples where there was considerable blight, the 
insects frequently visited the sweet, gummy exudation on infected trees. 
It is possible that in this manner they not only spread the disease in the 
larger trees, but also carried the bacteria to adjoining blocks of one-year- 
old apple stock, where infections occurred through the punctures made by 
them. 

During the month of July the tarnished bugs are most abundant on 
the apples, and as a rule the blight has become more prevalent with their 
appearance. In two large nurseries this was especially noticeable in the 
season of 191 2. The presence of the insects greatly augmented the spread 
of the blight. New infections continued to occur. After some time 
(about the middle of August), when the tarnished bugs left the apple 
stock, the disease subsided. Comparatively few new infections occurred 
throughout the remainder of the season, even though the trees continued 
for some time to make a succulent growth. 



The Fire Blight Disease in Nursery Stock 341 

Aphids. — The common green aphids (Aphis pomi) have also been 
associated with the blight disseminators, and their importance was espe- 
cially noticeable during the season of 1909 when there was an unusually 
severe aphid infestation on fruit stock throughout New York State. In 
one of the large nurseries considerable blossom blight had occurred in 
a block of two-years-old quince trees; and with the appearance of the 
aphids, not only did the disease become more abundant in the quinces, 
but the bacteria were carried to the blocks of apples. From all indications 
the blight followed the path of the aphid infestation, since no infections 
had been observed in any of the apples until after the appearance of the 
aphids. By dipping the infested shoots in whale-oil soap solution, seven 
pounds to fifty gallons, thus eradicating the aphids, the prevalence of 
the blight was soon greatly reduced. 

Jones ('09), in his studies and investigations on fire blight, is also 
led to conclude that aphids are important in the dissemination of the 
blight bacteria, both in the nursery and in the orchard. He suggests 
that possibly blight epidemics can be associated with years when aphids 
are unusually common. The writer, however, is inclined to the opinion 
that the occurrence of aphids does not play such an important part in 
the spread of the disease. Without question, when aphids appear in 
trees that are blighted, there is a tendency for the bacteria to be more 
widely disseminated; but a number of instances may be cited in which 
entire nurseries have been severely infested with aphids and yet practi- 
cally no blight has appeared in the same season. It is also an important 
point that periods of prolonged dry and hot weather are favorable to 
aphids, whereas such conditions can hardly be considered conducive to 
blight epidemics. Blight infections occur regularly only in succulent 
tissues, and in the nursery, especially, where the rapidity of growth is 
greatly decreased by such diverse weather conditions, it is not' to be 
expected that infections will occur so abundantly. However, the infec- 
tion experiments conducted by the writer during the winter of 191 1- 
191 2 in the greenhouse proved conclusively that blight infections do 
occur through aphid punctures in young succulent tissues. 

Shoots of three pear seedlings were smeared by means of a camel's- 
hair brush with an agar culture of Bacillus amylivorus, and a number of 
aphids {Aphis pomi) were transfsrred to these shoots. In the same 
manner shoots of two other seedlings were smeared with the agar culture 
of the organism, but no aphids were transferred to these trees. All the 
trees were covered with large bell glasses, and on the tenth day four of 
the aphid-infested shoots showed the characteristic symptoms of fire 

C09) Jones, D. H. Bacterial blight of apple, pear, and quince trees. Ontario Agr. Col. Bui, 176:1-63. 
1909. 



342 Bulletin 329 

blight. Of the shoots from which the aphids had been excluded, none 
blighted. In another experiment a number of aphids were smeared with 
an agar culture of Bacillus amylivorus and placed on the shoots of two 
seedlings. The shoots of two other seedlings were smeared with the agar 
culture as in the experiment above. All trees were covered with bell 
glasses, and on the eleventh day three of the aphid-infested shoots were 
blighted. None of the other shoots became diseased. Isolations were 
made from the blighted twigs and a pure culture of Bacillus amylivorus 
was obtained. 

When the aphids were present to puncture the tissue and thus furnish 
a means of entrance for the bacteria, about fifty per cent of the shoots in 
the above experiments became diseased. No infections occurred when 
the shoots were smeared with the culture of the organism and the insects 
excluded. The best results were obtained with the use of tender and 
succulent shoots, and no doubt the percentage of infections would have 
been greater had it been possible to select the tenderest growth in every 
case. 

Dissemination by pruning tools 

Besides the general distribution of the blight germs by insects, man 
himself is often an active agent in spreading the parasite. Pruning tools 
are certainly a frequent means of transmitting the organisms. Whetzel 
('06) has demonstrated this point, and the experience of others proves 
fairly conclusively that the disease may be transmitted by the tools in 
use. Waite ('06) states: " In Maryland the writer once saw a nursery 
block of 10,000 trees of Bartlett and other pears completely destroyed 
by blight. This block, as determined by the specimen, carried actual 
samples of hold-over blight in the stocks. When the stocks were cut 
off above the dormant buds in the spring, the pruning tools became in- 
fected and the disease was transmitted to nearly every tree reached by 
the pruners. Instead of the buds pushing up, the cut surface began to 
gum and blight." 

A somewhat similar incident occurred during the season of 19 10 in one 
of the nurseries of New York. A large number of scions of Kieffer pears 
were obtained from a nursery in Alabama and used for budding several 
thousand seedlings (Fig. 118). Some time later, when the block was 
being rebudded, a number of the stocks showed the characteristic symp- 
toms of blight in the region where the buds had been inserted. Other 
varieties were rebudded at this time, and after a period of about ten to 
fourteen days blighted stocks were common over the entire block. With- 

('06) Whetzel, H. H. The blight canker of apple trees. New York (Cornell) Agr. Exp. Sta. Bui. 
236 : 104-138. 1906. 

('06) Waite, M. B., and Smith, R. E. Pear blight. Ann. Rept. California Fruit Growers Assoc. 
31 : 137-161. 1906. 



The Fire Blight Disease in Nursery Stock 



343 



out question the disease was transmitted to other stocks from the seedlings 
budded with Kieffer scions, by means of the infected budding-knives. 
All indications were that the blight was first introduced with the Kieffer 
buds, which had no doubt been cut from diseased trees; and at rebudding 
time, the knives becoming infected, the spread of the disease was general. 
During the summer of 1912 the source of infection of a number of 
blighted apple seedlings, as determined by scions examined, was attributed 
to the use of diseased buds that had been cut from a block of two-years- 
old trees on which there had been considerable blight. Not only did the 




Fig. 118. — Budding pear seedlings 



seedlings blight which were budded with the diseased buds, but the 
bacteria were carried on the budder's knives to other seedlings. Later, 
at rebudding time, the budders, being unfamiliar with the disease, fre- 
quently attempted to rebud the blighted stocks, their knives became 
infected, and the bacteria were transmitted to other seedlings. The 
number of diseased seedlings was also increased when the strings used for 
tying the buds were cut. Frequently, in cutting a string a slight incision 
was made in the bark, and many trees were inoculated in this manner, 
the blight germs having been carried on the knives from the diseased 
stocks. 



344 



Bulletin 329 



Blight may also be introduced into the seedling block by means of 
insects that carry the bacteria to the tender shoots (Fig. 119). Occasion- 
ally entire trees become diseased in this manner. 
It is the opinion of the writer, however, that 
twig infections are seldom, if ever, so abundant 
in seedlings as to be the source of an epidemic. 
On the other hand, an attempt to bud any 
such infected stock would tend to favor the 
more rapid spread of the disease, the blight 
bacteria being carried on the budding-knives. 




Fig. 119 

apple seedling 



Special orchard considerations 
In general, blight infections in the nursery 
occur through the twigs and blossoms; in the 
orchard, however, infections are frequently 
produced in a number of other ways. Jones 
('11) has observed the work of a fruit bark-borer, 
Scolytus mgulosus, in spreading the blight in 
pear and apple orchards. 
Blighted shoot on In puncturing the 
diseased area the borer 
becomes infected, and later spreads the disease to 
healthy branches. In cuttings from a living 
branch of Bartlett pear, which was perforated 
by the fruit bark-boring beetle immediately 
below each of thirty leaf or fruit spurs, there 
was a beetle in every hole and the bark sur- 
rounding eight of these was developing blight. 
Occasionally the bacteria are introduced into 
green fruit by such insects as curculio, causing 
what is known as fruit blight (Fig. 120). 

Waite (1896) has observed instances in which 
sap suckers, becoming infected by puncturing 
cankers of hold-over blight, spread the disease to 
healthy trees. 

P. J. O' Gara is authority for a statement, 
published by Smith ('11) in his bulletin on 
crown gall, that fire blight cankers have been known to develop around 

(1896) Waite, M. B. Cause and prevention of pear blight. U. S. Dept. Agr. Yearbook 1895 : 295- 
300. 1896. 

('11) Jones, D. H. Scolytus rugulosus as an agent in the spread of bacterial blight in pear trees. Phy- 
topath. 1 : 155-158. pis. XXUI-XXIV. 191 1. 

('11) Smith, E. F., Brown, Nellie A., and Townsend, C. O. Crown-gall of plants: its cause and remedy. 
Crown-gall followed by hold-over blight. U. S. Dept. Agr., Bur. Plant Indus. Bui. 213 : 186. 191 1. 




Fig. 120. — Blighted apple. 
Bacteria introduced into 
fruit by curculio. Note the 
wound and the oozing drops 



The Fire Blight Disease in Nursery Stock 



345 



galls produced by the crown gall organism (Bacterium tumefaciens) on 
Esopus apple trees, the blight bacteria having gained an entrance 
through the gall. 

Whetzel ('06) has also noted it to be a common occurrence for cankers 
to develop on the trunk 
or the collar of orchard 
trees, the bacteria 
having gained entrance 
through a water sprout 
or a tender young shoot 
(Fig. 121). This point 
is of interest, since in 
the West, especially, 
the use of Le Conte 
stocks in preference to 
French seedlings has 
been advocated, owing 
to the tendency of trees 
budded on Le Conte 
stocks to sprout less 
from the collar of the 
tree. When French 
seedlings are used the 
abundance of sprouts 
affords a means of 
entrance for bacteria, 
and losses from blight 
are increased. 



Hold-over blight 

The general opinion 
has prevailed that 
blight bacteria remain 




Fig. 121.- 



Blighted water sprouts on trunk of large pear tree 

alive over winter only in those cankers that are more or less protected from 
drying out; also, that the number of hold-over cankers in which the organ- 
isms survive the winter is comparatively few. However, some evidence 
has been produced that under favorable conditions the parasite may live 
over in blighted shoots or twigs, as well as in larger diseased branches or 
limbs. Burrill (1882) cites a case in which a nurseryman experienced 

(1882) Burrill, T. J. Have we any new light on pear blight or yellows? Rept. Michigan State Hort. 
Soc. 1S81 : 133-139. 1882. 

('06) Whetzel, H. H. The blight canker of apple trees. New York (Cornell) Agr. Exp. Sta. Bui. 
236 : 104-138. 1906. 



346 Bulletin 329 

heavy loss due to the blight in grafts newly made that winter. Some of 
the scions stored for grafting purposes had evidently been cut from blighted 
trees. When the grafts were made with these scions the grafting-knives 
became infected, thus favoring the transmission of bacteria to the non- 
diseased grafts. 

Sackett ('n) has recently shown that in Colorado the blight organism 
lives over winter in small blighted pear twigs. Numerous isolations 
were made from diseased pear twigs in February and March, and the 
parasite was frequently obtained in pure culture. 

Isolations made in March by the writer from diseased twigs (less than 
one centimeter in diameter) of Bartlett pears, taken from an orchard 
near Newark, New York, gave about the same results as did those of 
Sackett. An attempt was made to isolate the organism from five blighted 
twigs, and a pure culture of Bacillus amylivorus was obtained from two 
of these. The organism isolated produced the characteristic blight when 
used for inoculating the tender twigs of quince trees growing in the green- 
house. 

In the same month, the fire blight organism was isolated also from pear 
seedlings that had blighted the previous season. The trunks of the 
diseased seedlings were about one half inch in diameter. 

Hold-over blight in budded seedlings is of special significance since it 
furnishes a source for early infection the following spring. More atten- 
tion must also be given to hold-over blight in small twigs and branches, 
which until recently has been considered of little importance ; for it is 
evident that these small cankers frequently furnish a means for existence 
of the bacteria over winter. 

Influence of weather on blight 

Weather conditions at certain times during the growing season are an 
important consideration in connection with the dissemination of blight 
in the nursery. Prolonged hot and dry weather in the early part of the 
season tends to check the rapid development of the young shoots, causing 
them to make a hard and woody growth. The terminal buds close up 
and cease growing. Such shoots are not so liable to infection, and usually 
epidemics of the disease subside somewhat during a hot, dry period. 
Later, with increased precipitation the growth of the trees is accelerated, 
and their tissues become tender and succulent and are naturally in 
a condition to be more susceptible to attacks of the causal organism. 

The spread of blight is also more noticeable in the infected trees after 
abundant rainfall followed by periods of hot, cloudy weather. The 

('11) Sackett, W. G. Hold-over blight in the pear. Colorado Agr. Exp. Sta. Bui. 177 : 2-8. 1911. 



The Fire Blight Disease in Nursery Stock 347 

tissues are gorged with sap thus favoring increased activity of the bacteria, 
and the disease becomes more destructive. 

Cultivation and manuring as affecting fire blight 

Horticulturists and pathologists generally agree that cultivation, and 
the application of nitrogenous manures or of any material that tends to 
induce rapid and succulent growth, favor the serious development of 
blight, at least in pear trees. However, it seems that this general opinion 
is based on observation alone and that no carefully conducted experiments 
have been made in order to determine anything definite on this phase 
of the question. 

Usually, blighted trees are more common among those growing in 
rich soil, and it is generally conceded that the condition of the tree has 
much to do with the amount of damage produced after the malady appears. 
As a rule, the more succulent the tree, the more severely it is attacked. 

In the account of an experiment in orchard fertilization conducted by 
J. P. Stewart ('12) of the Pennsylvania Agricultural Experiment Station, 
certain observations with reference to fire blight arc recorded. The 
trees in the manured plots, and those in general that had made the most 
rapid growth throughout the preceding four or five years, blighted more 
severely than did those that had not received such excessive manuring. 

Period of growth-actitity . — Observations and experiments made by the 
writer indicate that the most important factor influencing the spread of 
the disease is the period of growth-activity of the host plant. As shown 
by inoculation experiments subsequently discussed, succulence of the 
host tissue is essential in order to insure infection by the blight organism. 
For a period of time in early spring the new growth that develops shows 
practically no difference in its tenderness and succulence, regardless of 
the conditions under which the host exists. The young, tender shoots of 
trees growing in sod are as liable to infection as the twigs of cultivated 
trees. Later, with the lack of cultivation and fertilizers, trees in sod 
make a slower growth, and the new shoots become hard and woody and 
do not blight so readily as do those of trees that are well cared for, in 
which the period of growth-activity and succulence is extended throughout 
the greater part of the growing season. It is also natural to expect, 
under such conditions, that the damage to cultivated trees will be greater, 
when once attacked, than to trees that are less succulent. Abundant 
twig and blossom infection has been observed frequently on orchard 
pear trees growing in sod, but usually the blight does not progress so 
rapidly into the larger branches and limbs. 

C12) Stewart, J. P. Factors influencing yield, color, size, and growth in apples. Relation of fertili- 
zation to fire blight. Rcpt. Pennsylvania Agr. Exp. Sta. 1910-1911 : 467. 1912. 



348 Bulletin 329 

The importance of the period of growth-activity as influencing blight 
infection is strongly emphasized by the experiments conducted throughout 
the past few years. 

Experiment of igio. — Thirty two-years-old Bartlett pear trees were 
set in the plant-disease garden on the university farm in the early spring 
of 1 9 10. There were three plats with ten trees in each. Plat 1 was 
manured heavily with stable manure and kept well cultivated. Plat 2 
was cultivated, but not manured. Plat 3 was in sod in Roberts' pasture, 
which has not been broken for about thirty years; this plat received no 
manure nor cultivation throughout the experiment. 

During the summer of 19 10 plats 1 and 2 were each cultivated three 
times, and at the end of the season there was a noticeable difference in 
growth between the cultivated trees and those in sod. 

Experiment of igu. — In the spring of 191 1 plat 1 was again heavily 
manured, and both plats 1 and 2 had received two cultivations up to 
July 1 . At this time there were marked differences in the growth of the 
trees; those in sod had made but little growth and the new shoots were 
short, hard, and woody, with indications that the growth for the season 
was practically completed. In the cultivated plats the trees had made 
a rapid growth and the development of young, tender shoots had been 
abundant. Many of these were still very succulent, especially on the 
trees that had been manured and cultivated. . 

On July 5, under ideal conditions for blight infection — a hot, cloudy 
day following a heav y rain — all the trees were inoculated with a four- 
days-old bouillon culture of Bacillus amylivorus, recently isolated from a 
blighted quince tree. An effort was made to choose the tenderest twigs 
in every case and three shoots on each tree were inoculated. 

Five days later, when some of the infections had become apparent, 
considerable differences were noticed. No infections had occurred in 
the trees in sod, in which it had been necessary to make the inoculations 
into hard, woody tissue. Inoculations of the trees cultivated but not 
manured showed about twenty-five per cent of the twigs infected. Practi- 
cally all the inoculated twigs on the heavily manured trees showed 
infection, as yet indicated only by a water-soaked appearance and slight 
discoloration. Four days later the progress of the malady in the infected 
shoots was considerably advanced and about forty per cent of the inocu- 
lated twigs in plat 2 were diseased. Only two infections developed in 
the trees growing in sod. 

It was strikingly noticeable that infections occurred only in twigs that 
were still making an active growth, indicating that succulence of the 
tissue is the primary factor in liability to infection by the bacteria. The 
hard and woody twigs of trees growing in sod were more resistant than 



The Fire Blight Disease in Nursery Stock 



349 



were the tender shoots of cultivated trees. Judging from results obtained 
the following year, had the inoculations been made earlier in the season 
the number of infections for the trees in sod would have been greater. 

Experiment of igi2. — Early in the spring of 1912 plats 1 and 2 were 
again cultivated and plat 1 was manured. On May 28 the inoculations 
as described above for 191 1 were 
repeated. At this time the new 
shoots on all the trees were tender 
and succulent. But little differ- 
ence was apparent, except that 
the shoots on the trees in sod 
were shorter and not so 
numerous. 

After five days all the inocu- 
lated shoots in plats 1 and 2 were 
evidently diseased, and out of a 
total of twenty-eight inoculated 
shoots in plat 3 only three failed 
to blight. Later in the season 
(July 22) many of the trees that 
had been cultivated were badly 
blighted (Figs. 122 and 123), 
new infections had occurred, 
and the larger branches and 
limbs were diseased. On the 
other hand, the trees in sod 
(Fig. 124) were not so severely 
attacked, no new infections had 
appeared, and the blight had 
progressed only a short distance 
(about six inches) from the 
points of inoculation. 

In connection with the question 
of succulence as influencing the amount of blight in the nursery, it is of 
interest to note also certain differences in growth-activity for various 
kinds of pome fruits when grown under the same conditions. Pear 
trees especially make their most rapid development early in the 
season, and after the middle of July the shoots are, as a rule, too hard 
and woody for blight infections to occur. Infection experiments 
during the latter part of July in 19 10 and in 191 1 on the two-years- 
old pear trees in the nursery gave but few positive results. In the 
greater number of cases the inoculations were a failure. Inocula- 




Fig. 122. — Bartlett pear tree in plat 1, highly 
cultivated andmanured. The blight practically 
ruined the entire tree 



35° 



Bulletin 329 



tions were successful, however, when made as late as September 1 the 
same years on adjoining blocks of two-years-old apples and quinces. All 

trees had received the same amounts of culti- 
vation and fertilizer. 

It is believed that such a condition is a deter- 
mining factor with reference to the dissemina- 
tion of the blight bacteria by such insects as the 
tarnished plant bug. Serious outbreaks of the 
disease have occurred in blocks of apples and 
quinces where the rapid spread of the parasite 
was attributed to the presence of the tarnished 
bug. Although the same insects infested near- 
by and adjoining blocks of pears, practically 
no blight appeared. In the writer's opinion 
this is due to the fact that the shoots had 
passed their period of most rapid development 
and were not in a condition to be so 
readily attacked by the bacteria. 



Varietal susceptibility 
Opinions disagree 
considerably regard- 
ing the susceptibility 

„ „ , of different varieties of 

Fig. 123. — Bartlett pear tree 

in plat 2, cultivated but not pears to this disease. 

manured. Such trees did Bartlett and Flemish 

not suffer so severely when 

inoculated with the fire are generally reported 

blight orga n ism as did those as being most severely 

attacked and much 
more susceptible, in different sections of the 
country, than Kieffer and Seckel. Among 
apples, Esopus and certain crab varieties are 
known to blight somewhat readily; but the 
difference in resistance for other varieties is 
considered not so constant, most of them being 
more or less affected. 

However, from observations and inoculation 
experiments the writer is inclined to believe 
that for nursery stock, at least, but little 
difference is shown by the several varieties in 
their ability to withstand the attacks of the blight 





Fig. 124. — Bartlett pear 
tree growing in sod in 
plat j. The progress of 
the blight was very 
limited, only the tender 
growth of the inoculated 
shoots becoming diseased 



The enormous 
amount of conflicting data that have been accumulated on the question 



The Fire Blight Disease in Nursery Stock 



35i 



of varietal resistance of orchard trees to fire blight, indicate that only 
such factors as the source of infection, the abundance of disseminating 
agents such as insects, and the period of growth-activity of the host 
plants are the criteria to be considered in determining the difference 
in susceptibility. As far as is known, all varieties are attacked under 
conditions favorable for the development and propagation of the malady. 

Inoculation experiments . — Believing that any differences manifested are 
governed more by external factors than by a natural immunity of certain 
varieties, a series of varietal inoculations was conducted on quinces, apples, 
and pears. From the results obtained it is conclusive that the varieties 
inoculated showed practically no difference in their resistance to attacks 
of the causal organism. All were susceptible. 

In the table below are listed the varieties inoculated, the dates on which 
the infections appeared, and the total number of infections for each. A 
four-days-old bouillon culture of Bacillus amylivorus was used for all 
inoculations. This strain was isolated in August, 191 1, from quince. 
An effort was made to choose the tenderest growth in every case and a 
single shoot on each of five different trees of each variety was inoculated 
by pricking the tip of the shoot with a needle that had been dipped into 
the bouillon culture. 

TABLE 2. Varietal Inoculations of Bacillus amylivorus on Two- Years-Old 
Quinces. Strain No. 8. Inoculations Made August 13, 1912 



Variety- 



Number of infections and dates 
on which they appeared 



August 17 August 18 August 19 



Total 
number 
of inocu- 
lations 



Total 
number 

of in- 
fections 



Bourgeat* 
Champion 
Meech. . . 

Rea 

Bentley. . 
Orange . . . 



♦Nomenclature according to code adopted by the American Pomological Society in 1903. 

TABLE 3. Varietal Inoculations of Bacillus amylivorus on Two- and Three- 
Years-Old Apples. Strain No. 8. Inoculations Made June 18, 1912 



Variety 



Two-years-old 

Gideon 

Hyslop 

Ontario 

Late Strawberry .... 

St. Lawrence 

General Grant 

Fall Pippin 

Transcendent 

Martha 



Number of infections and dates on which they appeared 



June June June June June June June July 
23 24 25 26 27 28 30 



Total 
number 
of inocu- 
lations 



Total 
number 
of infec- 
tions 



352 



Bulletin 329 



TABLE 3 {concluded) 



Variety 



Number of infections and dates on which they appeared 



June June June June June June June July 
23 24 25 26 27 28 30 



Total 
number 
of inocu- 
lations 



Total 
number 
of infec- 
tions 



Two-years-old 

Excelsior 

Mann 

Westfield 

Early Strawberry . . . 

Bismarck 

Whitney 

Alexander 

Roxbury 

Sutton 

Quebec 

Tetofsky 

Jersey Sweet 

Sops-of-Wine 

Smith Cider 

Ralls 

Longfield 

Esopus 

Winter Pearmain* . . 

America 

Wolf River 

Red Astrachan 

Tompkins Kinf; 

North Star 

Munson 

Bethel 

Peck 

Missouri 

Porter 

Newtown Pippin. . . . 

Haas 

Red June 

Peach 

Oldenburg 

Yellow Transparent . 

Rhode Island 

Ben Davis 

Gravenstein 

Arkansas Black 

Yellow Bellflower. . . 

Winter Banana 

Baldwin 

Wealthy 

Bottle Greening. . . . 

Jonathan 

Opalescent 

Walbridge 

Red Canadaf 

Stayman 

Black Gilliflower. . . 
Rolfe 



Three-years-old 

Mcintosh 

Wagener 

Bough 

York Imperial 

Pewaukee 

Tolman 

Golden Sweet 

Boiken 

Winesap 

Golden Russet 

Fameuse 

Rambo 

Rome 

Northern Spy 

Northwestern Greening. 

Gano 

Maiden Blush 

Pumpkin Sweet 

Stark 

Twenty Ounce 



5 5 

5 5 

S 5 

S 4 

5 3 

5 4 

S S 

5 5 

5 5 

5 5 

5 5 

5 5 

S 5 

S 5 

S 5 

5 5 

5 5 

5 S 

S 5 

5 S 



* Winter Pearmain. Two rows inoculated by mistake, making ten inoculations, 
t Red Canada. Only three inoculations, by mistake. 



The Fire Blight Disease in Nursery Stock 



353 



TABLE 4. Varietal Inoculations of Bacillus amylivorus on Three-Years- 
Old Pear Trees. Strain No. 8. Inoculations Made 
June 19, 1912 



Variety 



Number of infections and dates on which they appeared 



June 
23 



June 
24 



June 
25 



June 
26 



June 
27 



June 
28 



June 
30 



July 



Total 
number 
of inocu- 
lations 



Total 
number 
of infec- 
tions 



Garber 

Kieffer 

Seckel 

Anjou 

Sheldon 

Vermont Beauty 

Angouleme 

Clapp Favorite . . 

Koonce 

Flemish 



In the above experiments the failure of some of the inoculated twigs 
to blight was attributed to the hard and woody condition of the tissues, 
rather than to any natural immunity on the part of the host. Varietal 
inoculations on pears later in the season did not yield such a high per- 
centage of infections. Some of the varieties had made a slower growth 
than others and were not so readily attacked by the bacteria. In com- 
paring tables 4 and 5, it is to be noted that the varieties included in both 
are practically the same and that in Table 4 all are shown to be susceptible. 

The later inoculations were made on July 8, with a five-days-old bouillon 
culture of the same strain of Bacillus amylivorus as was used in other 
experiments. The tenderest growth was chosen in every case and the 
tip of a single shoot on each of three different trees was inoculated. The 
condition of the twig as to succulence and tenderness was also recorded. 



TABLE 5. 



Varietal Inoculations of Bacillus amylivorus on Two-Years-Old 
Pear Trees. Inoculations Made July 8, 1912 





Condition of shoots 


Number of infections and 
dates on which they ap- 
peared 


Total 
number 
of inocu- 
lations 


Total 
number 
of infec- 
tions 


Variety 


July 
12 


July 
13 


July 

14 


July 
16 


Kieffer 




3 

I 
2 
I 

1 
1 







1 

1 
1 

1 




1 






2 


1 
















T 




I 






3 
3 
3 
3 
3 
3 
3 
3 
3 
3 
3 
3 










Wilder Early 


Medium tender 

Medium tender 

Medium tender 

Medium tender 

Medium tender 

Medium tender 

Hard and woody .... 
Hard and woody .... 
Hard and woody .... 
Hard and woody .... 




Angouleme 

Bartlett 


3 
3 





































354 Bulletin 329 

Natural resistance. — As determined by the experiments, all varieties 
of pome fruits tested were susceptible to blight when inoculations were 
made during the period of most rapid development of the trees. Instances 
may be cited, however, when certain varieties have shown to some degree 
a natural freedom from the disease. In the summer of 19 12 the blight 
made its first appearance at one nursery during the first week in June, 
affecting two rows of Transcendent (crab) at one end of a large block of 
two-years-old apples. The disease was practically confined to this variety 
for several weeks, spreading gradually to the three rows of Fall Pippin 
adjoining the Transcendent. About the first part of July, with the appear- 
ance of the tarnished plant bug the blight became epidemic and was 
spread over one end of the block. 

Bearing in mind that the varieties which suffered most were in the 
vicinity where the disease first appeared, a few comparisons may be made. 
Fall Pippin and Transcendent blighted badly. Other varieties severely 
attacked were General Grant, St. Lawrence, Late Strawberry, Ontario, 
Mann, and Smith Cider. The Martha (crab) immediately next to the 
Transcendent blighted to only a slight extent, and the same is true of 
Excelsior and Whitney. By virtue of their position, it is evident that 
these varieties were for some reason less liable to blight as brought about 
by natural infection. 

Due to the fact that the other varieties were somewhat removed from 
the center of the epidemic, no definite statements can be made concerning 
their liability to infection. From previous observations at different 
times, it may be stated that in general the Yellow Transparent, Golden 
Russet, Sutton, Alexander, Ralls, Fameuse, Wagener, Tompkins King, 
Rhode Island, Baxter, and Rambo are more often affected than Baldwin, 
Ben Davis, Red Astrachan, Oldenburg, and Gravenstein. 

It is not possible, however, to place much reliance on differences mani- 
fested by certain varieties in their liability to blight. The behavior of 
the trees toward the disease is no doubt greatly influenced by local con- 
ditions. This point is well illustrated from observations recorded by 
Crandall (1898) in Colorado. In a row of crabs, Martha and Whitney 
alternating, the Whitney trees were all severely attacked by the blight 
while not a single Martha tree blighted. It is interesting to note that in 
the nursery the Whitney variety was observed by the writer to be practi- 
cally free from the disease. The Martha also blighted to only a slight 
degree, although this variety has been known to blight readily in other 
localities. 

Special inoculation experiments 

Pathogenicity tests. — March 31, 1 9 1 2 . Inoculations of the nine cultures 
growing in bouillon which were used for the cultural studies were made 

(1S98) Crandall.C.S. Blight and other plant diseases. Colorado Agr Exp. Sta. Bui. 41:3-14, 1808. 






The Fire Blight Disease in Nursery Stock 355 

into shoots of quince trees growing in the greenhouse. Two shoots 
were inoculated with each culture. After ten days all inoculated shoots 
showed infections except those inoculated with culture No. 2, on which 
infections appeared one day later. It is of interest to note that culture 
No. 7, from Colorado, appeared to be the most virulent, the infection 
appearing afte? eight days; this culture gave the slowest reactions on 
the cultural media. Practically no difference could be noticed in the 
virulence of numbers 1,3, and 4, which were cultures isolated in different 
years from the same pear tree. 

Blossom inoculations. — February 23, 1912. Ten blossoms on two-years- 
old Yellow Transparent apple trees growing in the greenhouse were sprayed, 
by means of an atomizer, with a bouillon culture of Bacillus amylivorus. 
The blossom parts were thoroughly moistened with the solution and the 
blossoms were then covered for thirty-six hours with lamp chimneys 
stoppered with cotton. Checks were run by spraying four blossoms 
with sterile water. The checks were covered in the same manner as 
were the other blossoms. After nine days the inoculated blossoms showed 
symptoms of the disease, and after thirteen days the blight had not only 
involved the pedicels but was apparent in the older and more woody 
tissue of the blossom spurs. All the inoculated blossoms blighted; none 
of the checks became diseased. « 

March S, 191 2. Inoculations into quince blossoms on trees growing 
in the greenhouse were- made as follows: A small piece of absorbent 
cotton saturated with a bouillon culture of Bacillus amylivorus was placed 
in each of four blossoms. Care was taken in the manipulation not to 
injure any of the tissues. Two other blossoms were treated in the same 
manner except that the cotton was saturated with sterile water instead 
of with the culture of the organism. After ten days all the inoculated 
blossoms were blighted and the checks remained healthy. 

Blossoms were also caused to blight by gently brushing the nectarial 
surfaces with a camel's-hair brush that had been dipped into a bouillon 
culture of Bacillus amylivorus. 

Loss of virulence. — March 24, 1912. A culture of Bacillus amylivorus 
that had been isolated from pear in the spring of 191 1 was used for inoculat- 
ing some young pear shoots on trees in the greenhouse. When the 
infections appeared the organism was reisolated and obtained in pure 
culture. Bouillon cultures of the recent reisolation and also of the original 
culture isolated in 191 1 were inoculated into different shoots on the same 
pear tree. After four days the reisolated culture had produced an infection, 
but the twigs inoculated with the old cultures did not show signs of the 
disease until nine days' after the inoculations. From these results it 
appears that there is a tendency for the recently isolated cultures to be 



356 Bulletin 329 

more virulent and that artificial propagation seems to reduce the 
virulence to some extent. 

Pathological histology 

Historical. — Burrill (1881) appears to have been the first to study the 
effects of Bacillus amylivorus on diseased tissues. He states that " the 
most conspicuous changes that can be observed by the aid of the micro- 
scope, in the tissues affected with the blight, is the disappearance of the 
stored starch." He further states that " the cell walls are not dissolved 
or altered in any way except by staining, which sometimes takes place 
through oxidation, in the later stages of the disease." He observed that 
the bacteria occupy the lumen of the cells in diseased tissue, but he found 
it difficult to explain how they penetrated the cell wall. He further 
observed that in the tips of apple twigs diseased with the blight, all the 
tissues, even the xylem and pith, are invaded; but that in older limbs 
only the bark is attacked and the outer bark, or cortex, is usually first 
affected. The bast fibres are never diseased and the cambium frequently 
escapes invasion. 

Waite (1898) in more recent investigations, being unable to demonstrate 
the diastatic action of the organism on starch, holds that " its principal 
food consists of nitrogenous matter, sugars and probably, to some extent, 
organic acids, the very substances which occur in vigorous young growing 
tissues of the host." Bacterial cavities of considerable size are often formed, 
gorged with the viscid mass of the pathogen. Waite ('06) states further 
that " very often it has progressed much farther in the bark of the branches 
than appears on casual examination, for as a general rule it works only 
in the bark, leaving the mature wood at first unharmed. The sap, 
therefore, is able to continue to flow upward in the wood so that the leaves 
and branches, though girdled and doomed to destruction, may still carry 
their foliage or even mature their fruit." Such a condition as Waite 
describes may result in hyperplasia (Fig. 125) of the bark tissue above the 
lesion or diseased area, due to the accumulation of products formed in 
the metabolism of the tree. The girdling of the branch prevents the 
conduction of the products downward beyond the point of lesion. 

Tissues affected. — A microscopic examination of sections of young 
diseased twigs shows a necrosis of the cells and a somewhat shrunken 
condition of the tissue. The cells are plasmolyzed and stained brown; 
the contents, having lost all semblance of organized cell contents, are 
thick and amorphous. The blight bacilli are present in great numbers 

(1881) Burrill, T. J. Blight of pear and apple trees. Rept. Illinois Industrial Univ. 10 : 62-84. 1881. 

(1898) Waite, M. B. Life history and characteristics of the pear blight germ. Proc. Amer. Assoc. 
Adv. Sci. 47 : 427-428. 1898. 

C06) Waite, M. B., and Smith, R. E. Pear bl ; ght. Ann. Rept. California Fruit Growers Assoc. 
31 : 137-161. 1906. 



The Fire Blight Disease in Nursery Stock 



357 



in the intercellular spaces and to some extent within the cells. The 
cortical parenchyma is most severely attacked. Sometimes the cambium 
layer is affected. This is especially true of twigs in the more advanced 
stages of the disease and in larger limbs and branches. The bacteria 
may invade the pith and also the xylem tissue of young, tender shoots, 
but apparently the organism does not migrate for any great distance 
through these tissues. 

After their introduction into the tissues through a wound or an insect 
puncture, the organisms multiply 
rapidly and extend in all direc- 
tions from the point of entrance. 
Although the lateral development 
is often sufficient to girdle and 
kill large limbs or even whole trees, 
the spread of the organism upward 
and downward is greater, often 
being several meters. There is a 
breaking and splitting apart of the 
cells, with the formation of pockets 
that are filled with bacteria sus- 
pended in a sticky substance. 
This gummy material is presum- 
ably a mixture of the cell sap 
and the decomposed substances of 
the tissues that have been formed 
in the metabolic processes of the 
bacteria. 

Frequently, with the active de- 
velopment of the bacilli, ruptures 
or fissures are produced and the 
gummy material laden with the 
organisms fills these cracks in the 

bark and oozes out as the characteristic exudation previously described 
(page 323). The tissues around the lenticels are also invaded and 
with the breaking down of the cells the bacterial exudation occurs through 
these openings. In newly affected shoots the bacteria may invade 
only a small area of the cortical parenchyma in their lateral develop- 
ment, but proceed for some distance downward. On reaching a 
lenticel, or with the formation of cracks or fissures, the exudation may 
occur before any marked external symptoms of the disease are apparent. 
This is especially true in young, tender shoots, when the progress of the 
bacteria downward is very rapid. 




Fig. 125. — Pear limbs girdled by fire blight 
cankers, causing hyperplasia of the bark 
tissue above the lesion 



358 Bulletin 329 

In a recent paper by Miss Bachmann ('13) the results are given of a 
careful examination into the histological relations of host and parasite, 
and several questionable points are cleared up with reference to the 
migration of the organisms in the tissues. For these studies inoculated 
blossoms of pear, water-shoots of apple, young pear seedlings, young 
shoots of pear and plum, and fruits of pear and apple were used. 

Miss Bachmann states that " the first evidence of infection in the tissues 
of the fruit or shoot is a transparency around the point of inoculation, 
followed later by a browning in the same region." The transparency 
is attributed to the removal of air from the intercellular spaces, this 
being replaced by the liquid in which the bacteria live. By an examina- 
tion of stained and unstained sections of inoculated tissues it was evident 
that the large intercellular spaces of the cortex provide a ready path for 
the migration of the organism. It was found also that the bacteria 
enter the xylem tubes very readily near the apex of young shoots, and 
frequently the tubes may be so packed with bacteria that transmission 
of sap in such a region is apparently impossible. From the author's 
observations it is to be assumed that the entrance of the bacteria into 
the xylem vessels is near the apex of the shoot and their presence in this 
tissue at some distance below is due to their migration downward. The 
greatest invasion of the xylem by the organism is always near the apex 
of the shoot. 

A study of inoculated green fruits also indicated that the bacteria 
were most abundant in the intercellular spaces. The organisms seldom, 
if ever, enter the cells — at least, not before the death of the tissues. 
Miss Bachmann is of the opinion that the bacteria cause plasmolysis of the 
cellular contents and that the cells die owing to the extraction of water 
into the intercellular spaces, although chemical changes in the protoplast 
may accompany this loss of water. Bacteria were frequently observed 
between cells of tissue that still appeared perfectly normal. From this 
condition Miss Bachmann concludes " that the substances produced in 
the metabolism of the organisms are not at all strongly or quickly toxic 
in their effect on the cells." The film of liquid in which the bacteria 
move is not extracted in such amount that it precedes the bacteria to 
any extent. It is also considered possible to explain the broken walls 
and the formation of cracks or fissures on a purely physical basis, and Miss 
Bachmann suggests that " it may be that the osmotic pressure of the sub- 
stance in which the bacteria are found is sufficiently great to rupture the 
cell walls." 

Cavity formation. — The theory advanced by Miss Bachmann as an 
explanation for the splitting of the cell walls does not appear to be entirely 

C13) Bachmann, Freda M. The migration of 'Bacillus amylovorus in the tissues of the host. Phy- 
topath. 3 : 3-17. pis. I -II. figs. 1-2. 1913. 



The Fire Blight Disease in Nursery Stock 359 

satisfactory. It is difficult to conceive of any great osmotic pressure 
being exerted in such tissues. By the killing of the protoplasm the plasma 
membrane would become functionless and exhibit no further ability to 
reject or permit the passage of certain substances through it. Under 
such conditions, owing to the permeability of the cell wall, any pressure 
exerted outside the cells, due to increased concentration of the solution 
or to the excess extraction of water from the cells, would only cause the 
solution to pass back into the dead cells until an equilibrium would be 
established, the pressure outside and inside becoming practically equal. 
There might be a tendency to force the medium containing the bacteria 
farther along in the intercellular spaces ; but it does not seem to the writer 
that a pressure due to osmosis could be created which would be strong 
enough to rupture the cell walls. 

In a general discussion of bacterial actions on the plant, Smith ('n) 
states that " the gum diseases rupture the bark and ooze extensively on 
the surface. Pear blight does this also to a lesser degree. Some, perhaps 
all, of this class of bacteria reach the surface through fissures due to surface 
tensions set up in dead tissues by the parts still alive and growing." Pres- 
sure of sap in the tissues might be transmitted to diseased parts and favor 
the exudation of the gum; or, due to increased growth of surrounding 
healthy tissues, a tension might be developed sufficient to cause rup- 
turing of the dead cell walls. Such a tension could not, however, be 
correctly called surface tension. Surface tension, as such, could scarcely 
be said to have any influence on the splitting apart of the cell walls. 
The chief activity that could be attributed to it might be the rounding 
up of the cell contents of the individual cells as they shrink and dry up 
after plasmolysis. 

It is probable that the above phenomenon of rupturing of the tissue 
may be more closely associated with some toxic or enzymic reaction which 
as yet is unknown. In view of some of the recent work on enzymes it 
seems natural to incline toward the enzymic theory. 

Toxins. — With present knowledge it is impossible to state exactly 
how the killing of the tissue is brought about. Arthur (1886) has shown 
that solutions in which the bacteria were grown caused no rotting of 
green fruits when filtered. He used the sterile filtrate of a strong solution 
of blighted tissue for inoculating green pears. However, there always 
remains the possibility that the toxin, or substance which affects the tis- 
sues, may be destroyed (that is, absorbed by the filter or actually filtered 
out) in the process of separation, and by the removal of the toxin no 
deleterious effect on the tissue would be expected. 

(1886) Arthur, J. C Report of Botanist. Pear Wight. Rept. New York (Geneva) Agr. Exp. Sta. 
4 : 242-248. 1886. 

('11) Smith, E. F. Bacteria in relation to plant diseases 2 : 69. 191 1. 



360 Bulletin 329 

Following the method of study as outlined by L. R. Jones ('io) 
in his work on the enzymic production of Bacillus carotovorus, an 
attempt was made by the writer to isolate the enzymes produced 
by Bacillus amylivorus. But all tests for the production of diastase 
and the cell-wall-dissolving enzymes, pectinase and cellulase, proved 
negative.* 

An aqueous solution of the substance isolated apparently had no effect 
on sections of pear and quince shoots. It is to be noted, however, that 
the extractions were made only from bouillon cultures of the organism, 
and under such conditions it is possible that the toxins or enzymes that 
act on the tissues were not produced. It has been shown that the nature 
of the culture medium in which an organism is grown exerts an important 
influence in the production of certain enzymes. This point is especially 
emphasized by the work of Knudson ('11) on the production of the 
enzyme tannase. 

Miss Bachmann ('13), having observed fire blight bacteria in the 
intercellular spaces of apparently normal tissue, concludes that the toxic 
action of the products formed by the organisms is at least very slow. 
It seems evident, however, that with the presence of the bacteria in the 
intercellular spaces some toxic action is necessary in order to cause plas- 
molysis of the protoplast, with resulting extraction of water from the cells. 
The plasma membrane must be acted on in some way by a product formed 
in the metabolism of the organisms. The phenomenon could hardly 
be brought about by the action of the bacteria with products of the host 
outside the cells, resulting in such an increased concentration of a sub- 
stance that would cause plasmolysis of the protoplast. If there were a 
tendency for increased concentration in this manner, the process would 
be very gradual; and under such conditions, presumably the protoplasm 
of the plant would be able to adjust itself to the change and there would 
be no permanent plasmolysis. It is well known that the protoplasm is 
often able to overcome partial plasmolysis caused by increased concen- 
tration of solutions outside the cell. This is evident in the case of cells 
of Tradescantia, which are able to recover when partially plasmolyzed 
by a solution of glucose sugar. If allowed to remain in this solution, the 
protoplasm will gradually adjust itself to the concentration and revert 
to its normal condition. The writer is of the opinion that, in view of 
the fact that only a limited amount of work has been done along this 

* As previously mentioned (page 337), the cane-sugar-reducing enzyme, invertase, was isolated by the 
above method. 

('10) Harding, H. A., Morse, W. J., and Jones, L. R. The bacterial soft rot of certain vegetables. 
Vermont Agr. Exp. Sta. Bui. 147 : 243-360. 1910. 

Cn) Knudson, Lewis. Regulatory formation of the enzyme tannase. Science n. s. 34 : 219-220. 
1911. 

('13) Bachmann, Freda M. The migration of Bacillus amylovorus in the tissues of the host. Phy- 
topath. 3 : 3-17. ph. I-II. figs- 1-2- 1913- 



The Fire Blight Disease in Nursery Stock 361 

line of investigation, sufficient evidence has apparently not been produced 
to warrant drawing definite conclusions as to exactly how the bacteria 
affect the tissue. 

Penetration of cell. — Although in the majority of cases the greatest 
invasion by the bacteria is in the intercellular spaces, they do occur in 
the cells to some extent. As with many other bacterial diseases, it has 
been impossible to demonstrate how the organism gains an entrance into 
the cell. With no apparent openings in the cell wall that would permit 
the passage of the bacteria, it may be assumed that the bacteria push 
or dissolve their way through thin places in the wall or through pits by 
mass action. In support of this view the following is quoted from Smith 
('n) in his discussion of the bacteria in the cells: " The most striking 
example, perhaps, is the voluminous intracellular occupation in the root 
nodules of Leguminosae. Here the cells are often crowded with bacteria 
with no visible opening for entrance. They seem to enter by mass action, 
the bacteria being compacted into strands. Often there is a trumpet- 
like expansion where the strand touches the cell wall. The writer has 
seen what appears to him to be a similar dense occupation of unruptured 
cells in the bark of the pear attacked by Bacillus amylovorus. The 
particular tissue which shows this to best advantage is the pitted col- 
lenchyma toward the outer part of the bark. In a few cases it has seemed 
as if bacteria could actually be traced from one cell into another across 
a narrow pit, but of the absolute correctness of this view I have not yet 
fully satisfied myself." 

In sections of quince and apple bark the compacted masses of bacteria 
as mentioned by Smith have been observed also by the writer, but it 
has not been possible to determine whether this is the manner in which 
the bacteria enter the cell. There still remains the possibility that their 
entrance is due to some toxic or enzymic action which as yet has been 
overlooked. 

CONTROL 

From the time that fire blight first became known, many recommenda- 
tions have been given and experiments tried for control of the disease, 
but previous to the discovery of the causal organism, little advancement 
was made in checking the malady. When all was conjecture, with no 
direct evidence available, no sharply defined treatment could be expected; 
but with the classical works of Burrill, Arthur, Waite, and others, better 
knowledge of the disease was obtained, and since the appearance of these 
works more rapid advancement has been made in control of fire 
blight. 



('11) Smith, E. F. Bacteria in relation to plant diseases 2 : 77- 191 r. 



362 Bulletin 329 

tree-feeding 

Feeding the trees in order to make them immune, by the introduction 
of various solutions into the sap, has not as yet been definitely proved 
to be successful despite the claims of many manufacturerers of blight 
remedies. Bolley ('04 and '07) also claims to have cured trees suffering 
from blight by feeding them formalin and various other materials. It 
is to be regretted, however, that no definite statements with regard to 
the work have been published, except that positive results have been 
obtained and that the treatment requires too careful manipulation to be 
recommended to the general public. 

SPRAYING 

Spraying the trees with a fungicide is generally not considered effective. 
The very nature of the method of introduction of the causal organism 
into the trees precludes this in most cases as an effective means of pre- 
vention. Apparently the bacteria are unable to penetrate the cuticle 
of the host tissue, and can produce infection only when a means is afforded 
for their entrance into the bark tissue through a wound or puncture. 

It is to be noted, however, from the experiments in blossom infection 
previously described, that no injury to the host tissue was necessary 
when the bacteria were sprayed with an atomizer into the open blossoms. 
Waite (1898) makes the following statement with reference to blossom 
blight: " Beginning in the spring the germs on the new growth of the 
season first appear on the nectar disks of the blossoms. The bacilli live 
and multiply in the nectar and are able to enter the nectar glands without 
a puncture or injury and thus normally get inside their host." 

It has been suggested that spraying into the blossoms * might 
tend to decrease the amount of blossom blight, the fungicide serving as 
a means of prevention when the bacteria are carried to the blossom by 
insects. Unpublished observations made by Dr. Donald Reddick, of 
this Department, seem to indicate that spraying might possibly be 
effective in reducing the amount of blossom blight. On the other hand, 
apple blossoms on trees growing in the greenhouse were susceptible to 
blight when sprayed with lime-sulfur solution, 1-40, and the following 
day sprayed with a bouillon culture of Bacillus amylivorus. 

* In the State of New York it is a penal offense to spray vhen the trees are in blossom. This law was 
enacted on the assumption that spraying at this time was harmful to the bee industry: Section 1757. 
Penal Law. Spraying fruit trees with poison. Any person who will spray with, or apply in any way, 
poison or any poisonous substance to fruit trees while the same are in blossom, is guilty of a misdemeanor, 
punishable by fine of not less than ten dollars (Sio) or more than fifty dollars ($50) for each offense." 

(189S) Waite, M. B. Life history and characteristics of the pear blight germ. Proc. Amer. Assoc. 
Adv. Sci. 47 : 427-428. 1898. 

('04) Bolley, H. L. Tree feeding and tree medication. Ann. Rept. North Dakota Agr. Exp. Sta. 
14 : 55-58. 1904. 

('07) Bollev, H. L. Tree feeding and tree medication. Ann. Rept. North Dakota Agr. Exp. Sta. 
16 : 35. 1907. 



The Fire Blight Disease in Nursery Stock 363 

patent nostrums 
Certain manufacturers have placed blight remedies on the market, 
but as yet none of these have proved of value; in fact, in most cases those 
tested have been injurious to the trees themselves. The experiments 
of Whetzel ('09) with Callahan's blight specific proves conclusively that 
this substance is worthless as a blight remedy and even causes injury to 

the trees. 

During the summer of 19 10 three blight remedies were tried in the 
nursery, by the writer. California pear blight remedy, Warnock's tree 
paint, and Leffler's insecticide and blight remedy were the substances 
used.' All were applied according to the directions given. Although the 
experiment was not carried to completion and the treated trees were not 
inoculated with the blight organisms in order to test their immunity, it 
suffices to state that in every case the remedies proved injurious to the 
trees. With the California pear blight remedy and the Leffler's insecticide 
and blight remedy applied in solution form to the soil, the two-years-old 
Bartlett trees treated were stunted at the end of the season as compared 
with untreated trees. In some cases part of the foliage fell prematurely. 
The Warnock's tree paint caused a splitting and cracking of the bark 
and the trees were unsalable when dug in the autumn. 

It is suggested that the general use of commercial blight remedies, at 
least on nursery stock, be avoided except when tried experimentally on 
a small scale in order to test the value of the remedy. 

GENERAL PLAN OF CONTROL 

For the most satisfactory means of controlling fire blight, reference is 
made to the plan of operation outlined in a bulletin by Whetzel and 
Stewart ('09). Strict sanitation and an attempt to eradicate the disease 
from the locality affected are believed to be the most essential factors in 
the control of the malady. All sources of infection should be destroyed. 
A systematic inspection of all apple, pear, and quince stock should be 
made early in the spring, and trees with hold-over blight should be 
promptly removed and burned. 

Old orchard trees of pear, apple, and quince in the vicinity of the nursery 
usually favor the blight, in that frequently theselarge trees become diseased 
and for years are sources of infection for nursery stock. Unless such trees 
are given special attention and kept free from disease by strict control 
methods, their presence is usually a menace to the nursery. Judging 
from the experiences and observations of the writer, old neglected orchard 

Agr. Exp. Sta. Bui. 272 : 31-52. 1909. 



364 Bulletin 329 

trees should be removed from the vicinity of the nursery and every effort 
should be made to keep the surroundings clean and free from sources of 
disease. Old hawthorns and wild crab-apple trees along fence rows or 
in near-by pastures frequently harbor the blight. Such trees should be 
destroyed. Too much emphasis cannot be laid on the necessity for 
a thorough and systematic cleaning-up of all diseased trees before growth 
starts in the spring. 

A regular inspection of all orchard trees should be made at least once 
each week during the summer, beginning as soon as the blossoms fall. 
Cut out all blighted twigs, shoots, and water sprouts, disinfect the cuts 
with corrosive sublimate 1-1,000, and burn the prunings. If all cut 
surfaces are disinfected, any bacteria left on them by the tools or any 
brought to them subsequently by insects will be destroyed. 

A thorough cleaning-up and removal of all sources of disease in the 
early spring naturally reduces the possibility of blight infection in the 
nursery. However, as previously pointed out, bees and other insects 
frequently carry the bacteria from oozing hold-over cankers to the blossoms 
that often appear on the two-years-old quince stock. Since the pro- 
duction of fruit by such trees not only causes a stunted growth for the 
tree, but also furnishes a source of infection at blossoming time, it is 
considered good practice to pinch off or remove before they open all 
blossom buds from the two-years-old quince trees. 

CONTROL IN NURSERY STOCK 

Inspection 

The plan of operation described above was successfully performed in 
two large nurseries in 191 2. By the removal of the blossom buds it is 
believed that an early epidemic of the disease was prevented. This 
opinion is based on the fact that through oversight an occasional blossom 
bud was missed and was allowed to open. Later several of these blos- 
soms were blighted. The amount of blossom blight would doubtless 
have been much greater if the blossom spurs had not been removed. 

With the presence of the disseminating agents that greatly favor the 
spread of twig blight, thorough and frequent inspections of all susceptible 
stock become necessary in order to keep the disease under control. It is 
often necessary to inspect certain blocks daily, the diseased twigs being 
cut out as fast as they appear. In every case the cut surface should be 
disinfected with corrosive sublimate 1-1,000. For the work of inspection 
the equipment illustrated in Fig. 126 has proved very convenient. An 
ordinary pruning knive is used for removing the diseased twigs, which 
are carried away in a sack and burned. The supply of corrosive subli- 



The Fire Blight Disease in Nursery Stock 



365 



mate can be carried in a bottle, and the sponge used for swabbing the 
wound can be moistened from time to time. 

With thorough and systematic inspections the number of new infections 
can be reduced 
greatly, and often by 
prompt and careful 
work in removing the 
first infections an epi- 
demic can be averted 
completely. In cut- 
ting out new infec- 
tions it is advisable to 
remove the entire 
twig, making a clean 
cut at the trunk; this 
gives greater likeli- 
hood that all the 
blighted tissue has 
been removed. Severe 
pruning of the young 
twigs of nursery trees 
leads to a bushy 
growth rather than 
to the ordinary de- 
velopment of long, 
unbranched shoots. 
When the infections 
have progressed 
rapidly down the twig, 
extending into ths 
trunk of the tree, the 
removal of the entire 
tree is advisable. 

When budded stock 
of the first year be- 
comes diseased the 
blighted trees should 
be immediately grubbed out. Usually the bacteria are extremely 
active in such tender growth and the greater part of the tree is soon 
involved by the disease. Cutting back below the diseased area causes 
a crook in the trunk of the tree and such stock can seldom be put on the 
market. 




Fig. 126. — Cutting blight from nursery stock. Note the bag 
for holding the blighted shoots, the bottle of corrosive 
sublimate, and the sponge at the end of a string 



366 Bulletin 329 

The plan of blight control as discussed with reference to the removal 
of new infections under orchard conditions, as fast as they appear 
throughout the summer, has been questioned by some investigators. 
O'Gara ('09) has offered special criticism to this procedure. He is of 
the opinion that summer cutting is advisable where there is only a little 
blight in the orchards, but under other conditions the work is only half 
satisfactory. He makes the statement, apparently copied from a previous 
article by Waite ('06), " that summer cutting is generally a failure for 
the reason that new infections, invisible at the time the work is done, 
may develop in a few days, so that a week after the most thorough cutting 
out of the blight a new crop of infection is found appearing." 

If badly blighted trees are given only occasional attention during the 
summer, practically no satisfactory results in blight control can be 
expected. 

Data are presented in Bulletin 272 of the Cornell University Agricul- 
tural Experiment Station, which indicate that thorough, frequent, and 
systematic inspections of the pear orchard throughout the summer, with 
immediate removal of any diseased parts, will prove effective, under 
western New York conditions, in the control of fire blight. Observations 
made by various members of the Department of Plant Pathology at 
Cornell University, of practical attempts in control of fire blight, indicate 
that when the above recommendations are closely followed pear orchards 
may be saved. 

The experience of Gammon ('12) indicates, further, that cutting out 
the blight in summer is practicable also in the West, despite the claims 
of some investigators who have worked in that section of the country. 
The results of active effort for seven years in the control of the disease 
in a large orchard in California were highly satisfactory. Careful prun- 
ing and thorough disinfection throughout the summer greatly reduced 
the annual loss of trees. 

When the disease is once established its eradication is, as a rule, im- 
possible. However, by inspection, as previously described, the blight 
can be held in check not only in orchard trees but also in nursery stock. 
Frequently the removal early in the season of a single blighted shoot will 
prevent the loss of an entire tree. Cutting out infections not only pro- 
tects the remainder of the tree, but also eradicates a source of infection 
for neighboring trees. 

In tables 6 and 7 are included a careful estimate of the number of 
infections occurring in apples, quinces, and pears, and also the number 

('06) Waite, M. B., and Smith, R. E. Pear blight. Ann. Rept. California Fruit Growers Assoc. 
31: 137-161. 1906. 

('09) O'Gara, P. J. Control of pear blight on the Pacific coast. Ann. Rept. Washington State Hort. 
Assoc. 5 : 36-55. 1909. 

('12) Gammon, E. A. Pear blight control. Cilif rni i H >rt. Crjm. Mo. Bui. 1:37-41. 1912. 



The Fire Blight Disease in Nursery Stock 



367 



of blighted trees removed, in two of the larger nurseries in New York 
State. In each nursery were about 150 acres of apple, quince, and pear 
stock. This work in nursery control was conducted during the summer 
of 191 1, which was an epidemic year for the blight over the entire State. 
Frequent inspections were made and a record was kept of the number of 
infections cut out and the number of trees removed on each inspection. 
In blocks where the disease was very abundant — as, for example, among 
the two-years-old quinces — daily inspections were made until the blight 
subsided. Some blocks of two-years-old apples and pears were not in- 
spected more than once every four or five days. 

The greater abundance of blight in nursery A, as recorded in Table 6, 
is attributed to the fact that, with the presence of a large number of 
hold-over cankers on trees that had blighted in the previous year, a greater 
amount of blossom infection occurred in the two-years-old quinces. 
On the first day of inspection over two thousand blighted blossom spurs 
were removed. This condition naturally furnished an abundant source 
of infection for the blocks of apples and pears near by. In nursery B 
all hold-over blight had been cleaned up and the blossom infection of the 
quinces was not so abundant. Under such conditions the possibilities of 
checking the malady were more favorable. 

TABLE 6. Number of Infections and Number of Trees Removed, Nursery A 



Kind of stock 



Number 


Number 


of 


of trees 


infections 


cut out 


540 


40 


1 ,700 


800 


3.500 


290 


None 


None 


95 


None 


524 


10 


None 


None 



Apple (2 years old) 

Apple (1 year old) 

Quince (2 years old) 

Quince (1 year old) 

Pear (standard 2 years old) 
Pear (dwarf 2 years old) . . 
Pear (1 year old) 

Total 



6,359 



1 , 140 



TABLE 7. Number of Infections and Number of Trees Removed, Nursery B 



Kind of stock 



Number 


Number 


of 


of trees 


infections 


cut out 


10 


3 


69 


30 


236 


25 


145 


40 


None 


None 


45 


12 



Apple (2 years old) . 
Apple (1 year old) . . 
Quince (2 years old) 
Quince (i year old) . 
Pear (2 years old) . . 
Pear (1 year old) . . . 

Total 



505 



368 Bulletin 329 

It is evident from the above figures that a large percentage of the 
infected trees were saved by prompt pruning and disinfection before the 
disease involved the entire tree. This, of course, does not include the 
large number of other trees that were entirely protected from the disease 
by removal of the blighted trees and shoots that would have served as 
sources of infection had they been left. 

The four years of work for blight control in the nursery lead the writer 
to believe that it is highly profitable to give careful attention to fire blight. 
Eradicating the hold-over blight, removing quince blossom buds, and 
inspecting diseased areas systematically will reduce the abundance of the 
disease, without question. 

Destruction of insect agents 
The elimination of certain disseminating agents is an important con- 
sideration. It has been demonstrated that controlling the aphids is 
frequently an essential step in preventing the spread of the blight bacteria. 
The greatest necessity at the present time, however, is a means of 
eradicating from the nursery the numerous sucking insects that occur on 
stock that is susceptible to fire blight. Of these blight disseminators the 
tarnished plant bug (Lygus pratensis) appears at the present time to be 
the most important. 

BIBLIOGRAPHY 

The following bibliography is by no means complete. However, it 
includes practically all articles that are of importance. A large number 
of citations have been omitted because, on consultation, they have been 
found to be of slight consequence or to contain no points of advance in 
the knowledge of the disease. 

Adametz, L. Mikrococeen. Mikrococcus amylovorous Burrill. Mitt. 

(Est. Vers. Stat. Brau. u. Malz. 1: 30. 1888. 
Arthur, J. C. Diseases of pear. Pear blight. Rept. New York (Geneva) 

Agr. Exp. Sta. 3: 357-367- 1885. 

Pear blight and its cause. Amer. Nat. 19: 1177-1185. 1885. 

Proof that bacteria are the direct cause of the disease in trees 

known as pear blight. Proc. Amer. Assoc. Adv. Sci. '34: 295-298. 
1885. 

Pear blight, cause and prevention. Ann. Rept. New Jersey 



Hort. Soc. 1885: 1-16. 1 J 

Report of Botanist. Pear blight. Rept. New York (Geneva) 



Agr. Exp. Sta. 4: 242-248. 1886. 

History and biology of pear blight. Proc. Philadelphia Acad. 



Nat. Sci. 38: 322-341. 1887. 

Pear blight. Rept. New York (Geneva) Agr. Exp. Sta. 5: 275- 



289. 1887. 

Important articles on pear blight. Rept. New York (Geneva) 



Agr. Exp. Sta. 5: 300-315. ii 



The Fire Blight Disease in Nursery Stock 369 

Bachmann, Freda M. The migration of Bacillus amylovorus in the 

tissues of the host. Phytopath. 3 : 3-17. pis. I-II. figs. 1-2. 1913. 
Barry, Patrick. Insect blight. Genesee Farmer 8: 218. 1847. 
Beecher, H. W. The blight in the pear tree: its cause and a remedy for 

it. Mag. Hort. 10: 441-456. 1844. 
Bolley, H. L. Tree feeding and tree medication. Ann. Rept. North 

Dakota Agr. Exp. Sta. 14: 55-58. 1904. 
Tree feeding and tree medication. Ann. Rept. North Dakota 

Agr. Exp. Sta. 16: 3-5. 1907. 
Burrill, T. J. Pear blight. Trans. Illinois State Hort. Soc. 11: 114-116. 

1878. 

Fire blight. Trans. Illinois State Hort. Soc. 12: 77-81. 1879. 
Anthrax of fruit trees: or the so-called fire blight of pear and 



twig blight of apple trees. Proc. Amer. Assoc. Adv. Sci. 29: 583-597. 
1881. 
Pear and apple tree blight. Trans. Illinois State Hort. Soc. 14: 



157-167. 1881. 

Bacteria as a cause of disease in plants. Amer. Nat. 15 : 527-531. 



1881. 



Blight of pear and apple trees. Rept. Illinois Industrial Univ. 
10: 62-84. 1881. 

Have we any new light on pear blight or yellows ? Rept. Michigan 



State Hort. Soc. 1881: 133-139. 1882. 

New species of Micrococcus (Bacteria). Amer. Nat. 17: 319. 



1883. 

Pear blight and peach yellows. Trans. Illinois State Hort. Soc. 



17: 46-49. 1884. 
Chester, F. D. Notes on pear blight. Ann. Rept. Delaware Agr. Exp. 

Sta. 12:38-46. 1901. 
Pear blight and pear canker. Delaware Agr. Exp. Sta. Bui. 52: 

2-7. 1901. 

Treatment of pear blight cankers and inoculations. Ann. Rept. 



Delaware Agr. Exp. Sta. 14:40-43. 1903. 
Cook, A. J. Pear blight and bees. California Cultivator 17 : 83-84. 

1901. 
Cooke, S. S. Pear blight. Gardeners Monthly 9: 73-78. 1867. 
Coxe, William. Cultivation of fruit trees. Pear blight, 175-176. 181 7. 
Craig, J. Diseases of fruits. Apple and pear blight. Rept. Canada Exp. 

Farms 1896: 168-17 1. 1897. 
Crandall, C. S. Blight and other plant diseases. Colorado Agr. Exp. 

Sta. Bui. 41:3-14. 1898. 
Denning, William. On the decay of apple trees. Trans. New York 

Soc. Prom. Agr. Arts and Manfr. i 2 : 219-222. 1794. [Second edition 

i 2 : 185-187. 1801.] 
Eaton, L. C. Review of opinions of pear tree blight. Hort. 1: 459-463, 

495-500. 1846. 
Edwards, S. F. Bacterial diseases of fruits and vegetables. Bacterium 

amylovorus. Ann. Rept. Ontario Agr. Col. 32: 136-137. 1907. 
Ernst, A. H., and Downing, A. J. Fire blight in pear trees. Hort. 2: 

328-332. 1848. 



370 Bulletin 329 

Fulton, H, R. The persistence of Bacillus amylovorus in pruned apple 

twigs. Phytopath. 1:68. 191 1. 
Gammon, E. A. Pear blight control. California Hort. Com. Mo. Bui. 

1:37-41. 1912. 
Gookins, S. B., and Downing, A. J. Remarks on pear blight of the West. 

Hort. 1 : 253-256. 1846. 
Halsted, B. D. Report of Botanist. Experiments with pear blight. 

Rept. New Jersey Agr. Exp. Sta. 19: 352-354. 1899. 
Report of Botanist. Experiments with pear blight. Rept. New 

Jersey Agr. Exp. Sta. 20: 414-417. 1900. 

Report of Botanist. Experiments with pear blight. Rept. New 



Jersey Agr. Exp. Sta. 22: 430-433. 1902. 

Hull, E. B. Cryptogamous diseases and root pruning of the pear, a pre- 
ventive of blight. Trans. Illinois State Hort. Soc. 1868: 35-37. 1869. 

Isaac, John. Pear blight in California. Rept. California State Board 
Hort. 8: 53-65. 1902. 

Jackson, H. S. Fire blight of pear and apple. Oregon Agr. Exp. Sta. 
Cir. 7 : 2-16. 1910. 

James, J. H. Blight in pear trees. Mag. Hort. 15: 13-23. 1849. 

Jones, D. H. Bacterial blight of apple, pear, and quince trees. Ontario 
Agr. Col. Bui. 176: 1-63. 1909. 

Scolytus rugulosus as an agent in the spread of bacterial blight 

in pear trees. Phytopath. 1 : 155-158. pis. XXIII-XXIV. 191 1. 

Jones, L. R. Studies on plum blight. Centbl. Bakt. u. Par. 2,9: 835-841. 
1902. 

Jones, L. R., and Morse, W. J. Orchard diseases and their remedies. 
Plum blight. Rept. Vermont Agr. Exp. Sta. 15: 231-239. 1902. 

Lawrence, W. H. Important diseases of Washington. Fire blight. 
Washington Agr. Exp. Sta. Bui. 83: 19-21. 1907. 

Lowell, John. Pear blight. New England Farmer 5: 17-18, 42. 1826. 

Meehan, Thomas, and Hunt, J. G. Pear blight. Gardeners Monthly 17: 
245. 1875. 

Morse, W. J. Diseases of plants. Crotch injury caused by weather con- 
ditions. Maine Agr. Exp. Sta. Bui. 164: 18-19. 1908. 

O'Gara, P. J. Control of pear blight on the Pacific coast. Ann. Rept. 
Washington State Hort. Assoc. 5: 36-55. 1909. 

Control of pear blight on the Pacific coast. Better Fruit 5 2 : 

49-51,54-56; 5 5 : 30-43, 52-57. 1910. 

Orton, W. A. Plant diseases in the United States in 1901. Pear blight. 
U. S. Dept. Agr. Yearbook 1901 : 669. 1902. 

Disease resistance in plants. Ann. Rept. Amer. Breeders Assoc. 

1 : 202-207. 1905. 

Paddock, Wendall. An apricot blight. Colorado Agr. Exp. Sta. Bui. 84: 
5-14. 1903. 

An old orchard disease in a new role. Fire blight of apricot. 



Ann. Rept. Colorado Board Hort. 15: 75-77. 1904. 
Pierce, Newton B. Pear blight in California. Science n. s. 16: 193-194. 

1902. 
Sackett, W. G. Bacterial diseases in plants. Pear blight. Michigan 

Agr. Exp. Sta. Bui. 230: 205-210. 1905. 



The Fire Blioht Disease in Nursery Stock 371 

Some bacterial diseases of plants. Pear blight. Colorado Agr. 

Exp. Sta. Bui. 138: 6-14. 1909. 

Hold-over blight in the pear. Colorado Agr. Exp. Sta. Bui. 177 : 



2-8. 1911. 
Salisbury, J. H. Pear, apple, and peach trees affected with blight. 

Ohio Agr. Rept. 1863: 450-460, 469. 1S64. 
Shear, F. C. Apple twig blight. Garden and Forest 9: 467-468. 1896. 
Smith, E. F. Bacteria in relation to plant diseases 1:1-285. I 9°5! 2 - 

1-368. 1911. 
Smith, E. F., Brown, Nellie A., and Townsend, C. O. Crown-gall of 

plants: its cause and remedy. Crown-gall followed by hold-over 

blight. U. S. Dept. Agr., Bur. Plant Indus. Bui. 213: 186. 1911. 
Smith, R. E. Report of Plant Pathologist. Pear blight. California 

Agr. Exp. Sta. Bui. 184: 221-232. 1906. 
Report of Plant Pathologist. Pear blight. California Agr. Exp. 

Sta. Bui. 203: 18-24. 1909. 
Smith, R. E., and Smith, Elizabeth H. California plant diseases. Pear 

blight. California Agr. Exp. Sta. Bui. 218: 1154-1155. 1911. 
Snyder, Lillian. A bacteriological study of pear blight. Proc. Amer. 

Assoc. Adv. Sci. 47: 426-427. 1898. 
Stewart, J. P. Factors influencing yield, color, size, and growth in apples. 

Relation of fertilization to fire blight. Rept. Pennsylvania Agr. Exp. 

Sta. 1910-1911: 467. 1912. 
Taylor, W. A. Pear blight. Science n. s. 15: 990-991. 1902. 
Trevisan di Saint-Leon, Vittore. I generi e le specie delle batteriaceae', 

prodromo sinottico. Milano, 1-36. 1889. 
Waite, M. B. A remedy for pear blight. Science n. s. 1: 721. 1895. 
— Cause and prevention of pear blight. U. S. Dept. Agr. Year- 
book 1895: 295-300. 1896. 

Fungous diseases of the apple and pear. Proc. Michigan Hort. 



Soc. 1897: 1S6-191. 1898. 

Life history and characteristics of the pear blight germ. Proc. 



Amcr. Assoc. Adv. Sci. 47: 427-428. 1898. 
Relation of bees to the orchard. California Cultivator 18: 



390-391. 1902. 
— A new native host for pear blight. Science n. s. 25: 2S6-287. 

1907. 
Waite, M. B., and Smith, R. E. Pear blight. Ann. Rept. California 

Fruit Growers Assoc. 31: 137-161. 1906. 
Whetzel, H. H. The blight canker of apple trees. New York (Cornell) 

Agr. Exp. Sta. Bui. 236: 104-13S. 1906. 
Fire blight and apple tree canker. Ann. Rept. Wisconsin Hort. 

Soc. 36: 215-226. 1906. 
— Fire blight remedies. Proc. West. New York Hort. Soc. 54: 

119-126. 1909. 
Whetzel, H. H., and Stewart, V. B. Fire blight of pears, apples, quinces, 

etc. New York (Cornell) Agr. Exp. Sta. Bui. 272: 31-52. 1909. 
Whipple, 0. B. Pear blight. Colorado Agr. Exp. Staf Bui. 118:7-9. 

1907. 
Woods, A. F. The wastes of the farm. Pear blight. U. S. Dept. Agr. 

Yearbook 1908: 209. 1909. 



JUN 9 1913 



CORNELL UNIVERSITY AGRICULTURAL 
EXPERIMENT STATION 



The Following Bulletins and Circulars are Available for Distribution to 
Those Residents of New York State Who May Desire Them 



266 The black rot of the grape and its control 

272 Fire blight of pears, apples, quinces, etc. 

273 The effect of fertilizers applied to timothy 

on the corn crop following it 
283 The control of insect pests and plant 

diseases 
28s The cause of ' ' apoplexy ' ' in winter-fed lambs 
286 The snow-white linden moth 
289 Lime-sulfur as a summer spray 

291 The apple red-bugs 

292 Cauliflower and brussels sprouts on Long 

Island 
295 An agricultural survey of Tompkins county 

297 Studies of variation in plants 

298 The packing of apples in boxes 

302 Notes from the agricultural survey in 

Tompkins county 

303 The cell content of milk 

305 The cause of ' ' apoplexy " in winter-fed lambs 
307 An apple orchard survey of Ontario county 
309 The produ ction of " hothouse ' ' 1 ambs 



BULLETINS 
310 
313 



314 
316 

317 

318 
320 

321 
322 
323 

324 



325 
327 
328 



CIRCULARS 



Soy beans as a supplementary silage crop 

The production of new- and improved vari- 
eties of timothy 

Cooperative tests of corn varieties 

Frosts in New York 

Further experiments on the economic value 
of root crops for New York 

Constitutional vigor in poultry 

Sweet pea studies— III. Culture of the 
sweet pea 

Computing rations for farm animals 

The larch case-bearer 

A study of feeding standards for milk pro- 
duction 

A study of the biology of the apple mag- 
gut (Rhagolelis pomonella) , together with 
an investigation of methods of control 

Cherry fruit-flies and how to control them 

Methods of chick-feeding 

Hop mildew 



Testing the germination of seed corn 
Some essentials in cheese-making 
The elm leaf-beetle 
Orange hawkweed or paint-brush 
The chemical analysis of soil 
Propagation of starter for butter-making 
and cheese-making 



14 Working plans of Cornell poultry-houses 

15 Legume inoculation 

16 The imoroved New York State gasoline- 

heated colony-house brooding system 
(Departmentof Animal Husbandry circular) 
The formation of cow-testing associations 



Address 



MAILING ROOM 

COLLEGE OF AGRICULTURE 

ITHACA, N. Y. 



372 



LIBRARY OF CONGRESS 



015 793 617 7 




